I would go see an Osteopath maybe. It could be due to anything slight like posture, your chair, even sneezing. It may not be serious but if you leave it may get worse. A chiropractor should be able to sort you out and check things like posture and alignment. If it is a disc problem, a chiro won't be able to help much, but hopefully it's not. Either way, you need to get someone look at it. It's expensive (�40-ish for first appointment) but far better than a Doctor who will just give you pain killers and send you away.