Ain't that a biitch. Patella tendonitis has to be THE MOST frustrating knee injury out there b/c it just happens, you don't have to twist it or land wrongly to hurt it, it just comes out of nowhere. Anyway, I had patella tendonitis and had surgery to fix the problem. I would advise you to go to a doctor and let surgery be your final, final option because a lot of the time when you have surgery, it begets another problem. My patella tendonitis is completely cured but now I have this problemcalled patello femoral syndrome. (most likely it'll be cured in about a month) Basically it's a muscle imbalance in the quads that causes the patella to track wrongly, that could be your problem. It's also something you can see if you may have by just looking at your quads and knee when you bend down.
In order to cure that, you have to lifr weights that targets the VMO muscle (inner quad muscle), like leg lifts with the leg twisted out and foot pointed back, 1/3, 1/4th hack squats, and 30-45 degree leg extentions (ice afterwards), and such. If it hurts at all, stop doing it.
Anyway, go see a doctor first, get an MRI on the knee (I hope you have insurance or else it'll cost you A LOT, all I had to pay was 10 bucks on visits and my insurance covered everything else, even surgery) I had about 2 MRI's and did physical therapy and took some kind of steroids b4 I finally had to have surgery.
Also do a search on the internet for Active release therapy, and do a lot of stretching.
For the third time though, see a doctor first, b/c yours seems kind of weird. If anything, if you have tendonitis, ti would hurt more if you were running track (on concrete than anything else) and I didn't feel any sharp pain when I cut either, but I played basketball, not football.
