It may be a few things. It could be allergies, or it could of developed into a habit but most likely (as long he has no other symptoms) is that he's just still a little irritated in that area. Sure the sutures are disolved but I'm sure he has a little bit of scar tissue & not to mention whats on the inside. His tubes may still be healing or if the vet put any sutures inside of him they may still be disolving.
Is he licking the area so much that it has become irritated? If so then I would consult with the vet. But if he's doing great otherwise I'd wait a couple more weeks.