1. Weak foot MUSCLES that tire, and then the plantar fascia picks up the load.
2. Any of the calf muscles/tendons are too tight, the Achilles tendon being very a obvious one, and as you roll forward on your weak foot muscles plantar fasciitis gets strained.
The article about the calf raises the one guy posted is good because it's going to strengthen all the muscles and stretch. I did the same thing by doing barefoot step-ups on a flat chair 8 seconds down 8 seconds up. I've been doing that since my early 20s and I'm 58 now.
Right now you need to get rid of the scar tissue and strengthen your foot muscles. Every night when you go to sleep your body will be healing. But every morning when you get up you're going to break the new adhesions that come with healing.
Here's how I get rid of plantar fascitis in 2 weeks.
Bromelain enzyme, 1000 mg twice a day with water, must be taken between meals. Do that for 1 week. Bromelain is a unique enzyme derived from Pineapple stems and it is the key ingredient in meat tenderizer. It is used in Germany to treat heart attack patients to break up the scar tissue in their hearts. It is an anti-inflammatory and it also dissolves Scar Tissue when taken between meals.
After the first week take 500-1000 mg of bromelain 3 times a day between meals with water... 8 to 10 ounces of water should be fine.
Your body will be healing itself overnight so here's what you do in the morning. Wake up, remain in bed, spread your legs apart and bring your feet up so they touch each other. Use the heel of one foot to massage the full bottom of the other foot up and down, massage it well so that it gets warm. At least one minute on each foot.
When you step out of bed step into a pair of sandals that have a significant heel, moderate arch support and a soft heel pad. Wear them walking around your house and gradually warm up. Where them in the shower etcetera. Take them off and walk on the outside edges of your feet barefoot. Walk toes out and Toes in, dorsiflexing your feet curling your toes up towards your knees.
From the outside edges of your feet roll for gently curl your toes down and use the muscles in your feet, cannot rise up on your toes yet. Rock back and forth back and forth from heel to the balls of your feet standing on the outside edges of your feet. Keep walking around on your carpet on the edges of your feet toes and Toes out. As you warm up allow your feet to roll in... Gently.
Sit down and massage the bottom of your feet with the other heals just like you did in bed.
Make your way to the kitchen and take your bromelain with water... Making sure you do not have breakfast until 1-2 hours later.
Where are your heeled sandals in the shower on the hard shower floor.
Wear them out of the shower until you dry your feet and step into your heeled shoes.
You must also do complete hamstring calf foot linkage stretching.
When you stretch your hamstrings you'll do it with your leg elevated so it is perpendicular with your torso, forming a 90 degree angle torso and thigh.
You will not allow your hips to turn outward but you will keep them squared towards the front. You will Point your toes up and you will roll your foot left to right pulling your toes back gently. You will do this while keeping your hip square in order to get an equal stretch on the inner and outer hamstring muscles. When you are more flexible instead of using just your same side hand to pull your toes back you will be able to reach across your body with the opposite hand and Plum the outside edge of your foot while stretching your hamstrings at the same time.
Most people find the stretch enlightening, because they are stretching the IT band in the outer hamstring much more than they ever felt before. Also by keeping the hip square and the toes up and rolling the foot left and right you will feel a deep stretch out the long tendons from the small calf muscles, the same long tendons that go down and wrap beneath the foot and control pronation, or the sideways rolling of the foot.
Besides walking on the edge of your feet and what I described, have a flat wooden chair maybe with a thin pad, and using your bare feet, step up onto the chair and gradually rise up with your heel on the chair. Go up and down slowly, I do a count of 8 up and 8 down. 10 minutes would be quite a long time to do this you will find out!
As you warm up with the step up probably not the first day... But eventually you will be able to rise up on the ball of your foot a little bit at the top. But Don't Force It. I will come in time after the walking in bare feet strengthens foot muscles.
Remember the bromelain 3 times a day to break up the scar tissue.
Remember to massage when you first get out of bed and also if you sit in a chair for a long time you should can't just spring up and go walking across otherwise you will cause damage.
Get yourself a half foam roller, about 3 ft long. It's a firm foam to that has been cut in half to form a half moon profile. You're going to begin doing calf stretches by standing Barefoot with the balls of your feet up on it, and you'll be stretching your feet pointing your toes out and your toes in. You're going to bend your knees and lean over until you just begin tension, and then you will use your quadricep muscles to straighten your knees so that the opposing hamstrings won't relax and allow the stretch to occur. You're not going to lock your knees and then bend over... No no no. You cannot bend your knees slightly and bend over and then use your quadriceps to straighten your leg. You do it that way because using the quads automatically causes your brain to relax the hamstrings.
If you can't get a half foam roller just get a short piece of 2 by 4. But I recommend the foam roller because it has a little bit of give and instead of your plantar fasciitis getting over strained the foam will give and compress.
Remember you can do hot and cold water cycling in a swimming pool, and actually build your cardio to a superior level then perhaps even if you were running.
The above is what I've done and anytime I've had tenderness or an issue I'm able to get rid of it quickly.
Don't do the 1000 mg of bromelain more than 2 weeks because it should not be necessary. Just go to 500 mg three times a day.
And when you come back for God sakes don't be running on a sidewalk or Hard Road. Go on an astro turf field, or some smooth level grass. Always warm up carefully and cool down carefully.
If you wait too long to eat after workouts especially if you neglect enough protein and just enough carbohydrates your body will weeken.
If you're doing too many miles than your feet can handle, if you're losing the spring and your feet and the power and confidence feeling in your feet, if you keep going when that happens then you will reinjur your plantar fascia.
Commit to strengthening your feet. I had very weak feet growing up, I couldn't even finish a soccer game. But I overcame it and now I can run 16 miles at a pair of sandals on a hilly soft Trail.
Read over what I wrote and look at the key steps.
Be sure your nutrition is balanced especially green leafy vegetables. Stay off the hard surfaces as much as possible. Too much training on hard surfaces eventually robs your ligaments and tendons of their flexibility and you will gradually slow down, and as you have found, get injured.
I had a little bit of time on a Saturday so I just thought I'd pass on what I know. Good luck. Your passion for the sport should bring you success.