Back problems at 13?

i never sit up straight and always slouch. i make a conscious effort to sit up straight but then about 5 second later i find i'm slouched again. sometimes i will try to sit up straight as long as i can but after 30 secs m bike feels wierd and tired and i slouch again. any ways i've noticed my back is killing me latelt it hurts so bad. what could be causing this? could it be scoliosis? no one else in my family has this problem. what should i do abou this?