Why does my back get sore when i sleep?

Back pain: Do you have back pain when not in bed? Have you injured your back? If not, your mattress may not be providing the correct support for your back; old mattresses tend to sag in the middle; some new mattresses are too firm for your particular comfort. If pain persists, see fp for evaluation.

Vague: Could be a number of reasons. How long have you had this problem? Is it the bed? Have you tried sleeping in another bed? Do you have the pain with normal activities during the day? How is your posture and what kind of work/play do you do? I would see your doctor asap to try and determine the source of your problems.

Mattress problems?: Do you have pain only when sleeping? Is it upon getting up or while lying in bed? What position do you sleep in. Often times when you are sleeping your core muscles are at rest and you don;t have adequate support for your back if your bed is too soft. Is your pain only in the low back or do you have pain or other symptoms in your legs. I would try a more firm mattress and see your pcp.