el back

during races i have been getting some back pain, i mean real back pain. it has gotten progressively worse each race, and last race it really really hurt. it starts at about 20 minutes into the race and just keeps getting worse. last race i had a great first 25 minutes. right up there where i wanted to be, then the pain came. it hurts so much i cant't push it at all so i just fall back one place at a time. it sucks. at some points i could have breathed through my nose only. my legs werent tired either, its really frusterating since i know i can do a ton better.
i realized that i dont remember problems from before getting to school. and if it gets worse each race (does not hurt much at all in training), something i use every day is the problem. so either it is my mattress for my bed here, which i got replaced today. or my bike. which again if it does not hurt during trainging wouldnt make a whole lot of sense. so hopefully my new mattress will take care of the problem, if not i dont know what i am going to do.