Eh, my knee....

I didn't want to bring this up here, lest I seem like I'm whining, but apparently my dad's new insurance doesn't cover pre-existing injuries, and how am I supposed to tell the doctor that I hurt it wakeboarding in early January... Any who, oh great people here who have had knee injuries, I'm curious if anyone has any kind of ideas as to what I could have possibly done to my knee... Here's the description...

Back in early August, I talked my friend into letting me hit the water one last time before we went in, promising that I'd do a backroll (first day trying them). So I go up, almost land the first one, and then try again. Well on this one, I went fairly big, bigger than I usually do, landed in the flats and lost the board out from under me. When that happened, pain shot through my knee, and I sat in the water debating riding again. It killed my knee to be bent like it was floating in the water, but we decided that I should get up and see how it felt on the board. I got up, and when I was riding it didn't hurt at all and felt completely stable. Since then, keeping my leg in one position for too long (mostly straight, but bent sometimes) makes the knee stiff, and it's hard to bend. Stability didn't really exist in it during that time, but I also was avoiding walking on it, so I didn't pay much attention. Later the constant pain went away (with the help of ibuprofen), and turned into the occasional dull ache when I walked across campus or left the leg stiff. I went to the doctor at the school, she did all of the little flexibility tests, and one, either I didn't mention the pain because I hate admitting to pain to doctors and stuff or I just didn't feel anything when she did the stuff. She told me to stretch it and stuff at night, so I did. It seemed to work at first, but the pain never went away, even after a month of stretching every day. One day a 300 lb guy jumped on my back, and where I'd normally collapse (it's happened before...) my knee completely gave out, and when I fell it rotated, and I was hopping around on one foot the rest of the night. Go figure, of course, I fell out of this habit and my knee all but stopped hurting. Then it turned cold, and the dull ache's began again. When I came back home from school on break, I found that my knee was toast when I worked, and where I constantly rocked back and forth on it as I stood waiting to tear tickets, it lost stability. Within an hour of my work shift starting, I couldn't really bear to stand on both legs, and even then it still hurt. Lately, I've found that it isn't stable when I do most activities. I can't pinpoint where the pain is, because the throb just resonates through the entire knee and the surrounding parts of my leg. My friend who had to study physical therapy because he plans on being a football coach told me that it sounded like it could be a sprain, because I definitely did not tear it (it didn't swell up, and I could still walk), but yeah.

Any ideas on what this could be? Sorry for the long winded story, that's almost five months of unidentifiable symptoms...