The last four weeks I have been having problems with both my patellar tendons, specifically the area where they join to the shin bone. This area usually feels somewhat uncomfortable, but not totally painful, at the beginning of a run, and by one or two miles I no longer feel it at all. However, the pain becomes worse after stopping and even more severe when starting again. So you can imagine interval workouts are hell, and I usually can't finish them since by about halfway through I cannot run at all without extreme pain.
I took some time off from high school XC to try to fix this with lots of icing and stretching, but whenever I tried to come back the pain returned and I had to take more days off. It ended up being about four weeks with no racing and very low mileage. Last weekend I was able to run a race again, and during the race itself I didn't notice the knee issues, but the warmup was uncomfortable and I was hurting bad during the cooldown.
The problems started around the time I switched from Saucony Kinvaras to NB Zantes, which have a softer and slightly taller heel stack. My coach noted that I was starting to heelstrike again, even though I broke that habit last summer. I also started doing squats with weight for the first time, and my form was probably not very good. Over the last few weeks I have improved my squat form and stopped overstriding, in addition to stretching more than I used to, but the knee stuff still hasn't gone away.
It sounds like it might be Osgood-Schlatter's or maybe patellar tendonitis, which I have heard is fairly common for runners my age (16). If I can't figure what the problem is soon, I'm going to see a doctor. Any advice would be appreciated.