It is better to go the doctor for back ache. I cannot suggest anything except to wear a belt called lumbosacral support & take calcium tab.
You did not write that how much & what you eat?
Cut down your food to half. Leave all junk food.
Take plenty of water.
Leave all sweet can eat only fruits & veggies.
Play & join a team to play regularly.
Inshallah you will become smart.