My back is killing me?

my lower left side near my left thigh is killing! it started this morning during gym and every thursday theres this thing called "straw run" and we have to run trough the gym and trough the halls and back trough the gym again and when i was with my friends during straw run (this may sound funny but tis question is not a joke) we where goofing of during the hallway then i began to skip on my left leg and calling my self a "gangsta unicorn" (cause i was hyper) then after acouple times of duing that it began to hurt and the pain of course didnt keep me down although i was decreaseing speed so i useally get 12 but i can't belive i forced my self but i ended up with 16 more the usally and now its killing me and for tomarrow i need to turn in a ignment and i want to turn it in on time so i want to be at school tomarrow andon satrday my sister is having a quincinara and im a chambilan and i dont want to ruin the waltz so now i think im screwed beacause i can't bend over not lay down on the ground ! anything to help me by tomarrow?