I had the same experience with stitches in my mouth years ago, and more recently on a small incision made on my scalp. Yes, I think that could be the problem. Depending on the type, it can be up to 4 weeks for them to dissolve. Will he let you look in his mouth since it has been a week since you saw the vet? You are almost at 4 weeks? All you can do is to keep an eye on Gus and if he seems to be in discomfort take him back for a reevaluation. I suppose it could be nerves becoming a little reactive or something obscure, but he was fine for a while and now seems in some discomfort.