I've had this issue going on for a little over a year now. Your experience and symptoms sound similar to mine. I got a new job that has me sitting at a desk for 8-9 hours a day and I stopped running when I started the job so I was spending almost all my time sitting down. It was only after I started running again that I noticed the issue. For me it seems like a lifestyle issue that running simply exposed. Time off from running didn't help or hurt. The issue remained.
I tried a lot of different things (chiropractor, physical therapy, time off hoping it would heal itself) but here's what I've been doing the last month which has resulted in my biggest improvements since I first noticed this issue:
-Try standing at your desk when possible. I don't stand all day but I'll try standing when I notice I'm getting uncomfortable in my seat. And if you have to sit then focus on good posture (Also, find a comfortable chair and make sure you have it adjusted properly).
-Every 2 hours (at least), stand up and lightly stretch out. I have a nice routine now that only takes 5 minutes and since I started doing it I've felt much better during the day.
I'll usually start by putting my hands on my lower back and lightly bending backwards, pivoting at my hands. I hold for a few seconds while exhaling then return to normal standing position to recover for a few seconds. Repeat 10 times or until you feel like you got a good stretch. Next, I bend over at the hips, keeping my knees slightly bent, and reach to my toes while relaxing my lower back and shoulders. It should feel like your butt is sticking out. Make sure you're relaxing in your upper body and really bending at the hip. Hold this for 30 seconds or longer if you're feeling good. I'll usually end with some side leg swings using my desk to keep balance. Sometimes I'll throw in some single-leg calf raises just to get the blood flowing a bit and work on my lower leg strength and balance (Something I noticed that I lost since this issue started). Again, keep things light. You'll be stiff from sitting down for awhile. This is just meant to get things a little loose.
-If you can, try walking at lunch. It gets the legs moving and gets you out of a chair. Plus fresh air, sunlight and clearing your head is always nice in the middle of a work day.
-If you drive to work, and especially if it's a long commute, then make sure your car seat is adjusted properly. So much of this issue was the result of lifestyle problems. If you're sitting all day and not sitting properly then you're going to mess yourself up.
-Look up some good hip exercises and do them at least 3 times a week. Focus on getting the glute working. Make sure you do them on both legs too. Might seem obvious but some people might focus on the bad leg and ignore the good leg which can lead to more issues. After these exercises, make sure you stretch the hip. Don't over do it but you have to loosen it up. I've started to do some light beginner yoga exercises at night to also help open things up. It really helps after a long day to loosen up some stiff and achy muscles.
We might not be experiencing the same thing, but it sounds similar to me so I just figured I'd share what I've been doing that has led to some improvements. The main issue just seems like the muscles became weak and stiff and now the system stopped working properly. My focus has been on getting the muscles in my glute and hip stronger, loosening things up, and trying to get the muscles in my leg working together again.
Also keep in mind this was an issue that developed gradually due to changes in your lifestyle. The recovery process will be similar. It was tough for me to accept at first. I was just hoping a chiropractor could snap me back into place but it doesn't work like that. You need to be patient. I'm still learning this. Again, I don't know if what I'm doing will permanently fix things, but it has helped me feel a little better and that's the best I got right now.