I think you need to go and see your doctor to get this checked out !!
It may be nothing but at least your going to have peace of mind. It could be a number of diffrent things, but a doctor would be able to answer your question straight off.
I would also stop having sex, till you get checked !! Plus cut down on drinking coke and coffee so on as this is also a side effect so im told to make problems like this.... But doctor I feel is the only way forwards for you.