Lower back pain – what is it?

a couple months ago during the track season i tried high jump for the first time. i’m mostly a sprinter so i’d never done it before. but soon after i started, i developed a pain in the muscles of my very lower right back. i had to quit high jumping because it hurt so bad when i did it. now it’s soccer season, and it’s coming back. i’ll do some hard quick moves, and get in a postition to shoot, then my back just spasms and gets messed up and throws me completly off, and it hurts to continue playing. i’ve thought about it; it seems to only to hurt when i do quick things with my feet (like jumping off my right leg in high jump and moves in soccer)

so i’ve done a lot of different hamstring streches, and it seemes like it streches that muscle (muscles?) really well. yet when i get out there and play, it just starts hurting again. i feel no pain in my legs, just a small region in my back and it hurts bad. i have my first games of the season coming up this weekend, is there anything anyone knows about this? i’ve checked out all the lower back pain things on this site, and none of it sounds like what i have. please help!