Posture can be one factor. another is if you go to school, if you have a bag or rucksack thats heavy and you have it on just one shoulder instead of distrubuted weight, this can also cause back issues. there is no harm speaking with your doctors, going though what you do in the day, and it might be a simple case of sitting more upright, or theres centres that do physio exercises which can help improve your back.