running injury?

hi, i was wondering if someone could help me figure out an unknown injury. i recently got into running because i found that it was something i enjoyed. last thursday i finished a run, took a shower, and headed over to class. as i was walking to class i took a step down on a street curb and felt something in my left butt cheek (lol) pop. after that i was in a horrible limp for the rest of the day, and now (monday) i'm still feeling the pain and still have a little limp going on. it could be an incorrect assumption and all the blame may just go to me stepping off the curb wrong, but i'm going to assume that my run had something to do with this injury, even though it occurred about 45 minutes afterwards. my question is, does anyone know what i pulled or if it's serious? or do i just have to give it some time? i guess i'm worried because it's been a few days and i've only seen very little improvement.

i know i should see a physician, but that's a last resort for me since i have no insurance and am not in the best financial situation.

edit: i'm sorry, i put this in the wrong forum channel. you can delete it if you want.