Bruno is a male, six months old. For the past couple weeks, one of his nipples on the left side is 6-7 times larger than all of his other nipples. It's a little pink, but doesn't look that bad- just really strange. It looks uncomfortable, but it doesn't seem to bother him if I touch it or apply pressure. Is this normal or a sign of a major problem? We have an appointment with the vet in about a month, but should we go to the emergency vet?