I've never kept a skink, and do not know if they shed, because an infected molt would be my first guess.  How sure are you it is a male?  I know that in female reptiles, sometimes eggs can be produced and not laid, causing serious problems.  It may also be a tumor or an abcess.  If the lump is hard to the touch it is more likely a tumor, if it feels soft or squishy it is likely an abcess or cyst.  I can imagine it will be difficult to find a vet for reptiles but keep looking.  Without being able to put hands on the animal, it's hard to be of any real help!

Good luck!