It might be a kidney infection. I've had them before and it can feel like mild back pain. My buddy, who is a doctor, told me to flush them with cranberry juice or take cranberry pills that you can get from a health food store. It sounds bad, but drink about a gallon a day for 3 or 4 days. You[ll get sick of the taste and be pissin' like a race horse but it does a great job of flushing the kidneys.

It can't hurt.