Swelling near vent?

[Arconna]

One of my geckos has been having some shedding issues as of late and then I noticed this bulge just above his vent and I'm a bit concerned here. There was some unshed skin around the section where his little spikes are and still is (I stopped trying to get it off for now because it was bothering him quite a bit). I'm concerned because it looks bad and I'm not sure what it is.

Picture at the end. Anyone know what might be going on? Is this an infection?