pinched nerve in knee?

double post because i posted in wrong catagory


this has been and on going problem for over a year and is not constant
feels like i have a pinched nerve in the middle of my knee, it will only happen for a split a second
but the pain will bring me to my knees sometimes
it happens usually when im not using knee i.e. laying down, standing still and nothing specific triggers it
i have tried to pinpoint the area but all i can get from that is below the knee cap, in the middle, moving cap doesnt do anything
i know an xray would help find a problem but i have no health insurance


thanks in advanced