I've suddenly come up in red patches,possibly blistery,hard to tell. They do look like the start of mouth ulcers.They are inside my lower lip,at the point where teeth would hit inside if I bit my lip.I have a tendency towards mouth ulcers but this seems different,less painful so far and bigger-someone suggested it could be herpes,can you get that inside your mouth? I thought they were external. I'm worried as if it is herpes I obviously need to be super careful around the dcs as don't want to pass it on.I've never had a cold sore so have no idea about them. How can you tell the difference? I feel a bit foolish going to the GP with a mouth ulcer.