How do i come back after extensive knee surgery?

so last football season i was the starting tailback for my highschool football team. for the first three games i had a ball carry average of 27 yards. with over 30 carries per game. however in the third game i took a cheap shot to me right knee. i sat out the 2nd and 3rd quarter and went back in at the start of the 4th. i was pull out though cuz i couldnt run full steam. i practices for the next week but the pain persisted all over my leg. i went in after sitting out the next week of practice, my pain just got worse but i was still able to walk, i had figured i just bruised it bad. well i fractured my knee n 3 places, tore my lateral calateral ligament and tore several different tendons. the doctor placed me for immediate surgery. they made a 7 inch incision and 3 orthroscopic incisions. i had to have donor tendons and partial donor ligiments placed in me. my surgery took place oct 21st 2009. i've done pt and started extensive work outs for this season, practice starts tonight. however, when im on my leg for to long i get sharp pains? i can only run about 2 miles without it hurting and i cant walk around a theme park all day without severe pain. wat can i do to gear up better for football. i was looking at a full scholarship for athletics, but now if i dont get my knee right, i may not even b able to play college football, any suggestions? btw i was released from my physical contact restrictions last month, the doctor said i can now be involved in full contact sports without hurting it....wat should i do?