...seriously, guys?
OP: "Hey Doc, my book bag is too heavy so my back hurts!"
Doc: "...kid, get out of my office (after you pay cash for this consultation."
>>1 Just get a small travel bag on wheels for school that you can easily drag a few steps behind you. If anyone makes fun of you for it, just laugh in their faces and tell them they're the stupid ones for carrying around books that heavy.
...yeah, that's basically how I got through my freshman year of high school. LOL. My back couldn't handle the books at all .-.
But if you're getting back pain all the time without it, then go see a chiropractor, not your base doctor. Chiropractors will loosen the muscles in your back and tell you if there is any issue a lot faster, cheaper, and more efficiently than a regular doctor would. Just make sure your parents look up reviews and such because a bad chiropractor can make your back worse rather than better.
Bring it up to your parents. If they say they can't afford it, then try looking up back stretching exercises online. Just make a few general searches about relieving back pain and there should be plenty of temporary fixes that you can try out at home.