What is wrong with my right leg?

Gonococcal arthritis. Does it burn when you pee?

Show the video how you run: front view, back view and side view, especially how you put foot on the ground for form analysis

Sure, no problem. Here are 3 vids for front, back, and side. Change the playback speed to 0.25 speed to watch in slow motion.

Your left leg feels like it's longer than your right leg. In any case, the right leg is more straightened at the moment of landing, and the left leg is more bent at the knee joint. This is what immediately catches the eye.

almost all kneepain stems from hip instability.

You stretch with your right foot to the ground, even the body leans slightly on this leg. Go to an orthopedist, let him look at your posture from behind, he can immediately see if there are any anomalies by the level of the pelvis and heels, and also let him check the flat feet transverse and longitudinal.

Let's see what he says, if everything is fine, then it happens that one of the small muscles of the stabilizers is weak and can incorrectly turn either the foot or the thigh, then you need to identify which muscle group is weak and pump them. For example, sometimes the piriformis muscle wedges on my right leg and it begins to twist my hip joint a little due to a spasm of this muscle, and this immediately affects the outside of the knee (the ligament begins to ache) and also on the foot. But I already know this and with the help of strength training and massage I successfully cope with it.

In the early days I was able to run 70 miles a week for months without a single issue. All at easy pace or tempo.

When I later dropped down to 40 miles a week and started doing intervals, all hell broke loose.

Sorry I have no answer except to take glucosamine and vitamin d.

What should I do if it is not an option to go see an orthopedic doctor? I just did a few at-home mobility tests, and found that my hip mobility and strength is not good. Along with this, my core is not very good. I had difficulty with a one legged squat (not pistol squat), where I was unstable and my knee caved in on both sides. Also, for some reason, I can’t even do a deep squat, I fall backwards every time. Seems to me like there are a lot of issues that I need to fix. What are some ways I could fix these instabilities and imbalances?

Are you ok? Visit a doctor, whats a problem? This is your health... come on.

Do the Myrtl Routine every day (look it up online) to help with flexibility and range of motion in hips and glutes.

Then you need to lift weights twice a week to strengthen your muscles. If you want to keep it really simple do 3 sets of 10 reps with 60 seconds rest, then do the following routine: 1 squat exercise, 1 hip hinge exercise, 1 lunge exercise, 1 push exercise for chest, 1 pull exercise for your back, and 1 shoulder exercise. First 2 weeks use the lightest weight available to learn the movements and proper form. The upper body exercises need to be compound exercises (look it up). This is a decent starting point and you can refine it later and maybe even add exercises as you get better.

Also, the research suggests that runners should wait at least 3 hours after finishing a run to start lifting weights. And with weights you need to warm up and coll down with 5-10 minutes of cardio, preferably non-impact (so not running).

Awesome, that sounds like a great routine. I'll start it immediately. Thanks for the help!