I hurt my back help???!!!?

i hurt my back lifting heavy boxes, i lifted with my back instead of my legs...this was three weeks ago and it's getting worse... i ride a bike to class everyday (3 miles there and 3 miles back), i can't bend over easily i look like a pregnant woman (no offense) trying to bend over and get up easily i fight and struggle to get up...it's just painful,and i'm 18! and at school the desk makes it hurt more....what should i do should i apply heat or ice or something else....