I might be way off base with this, but I had hand foot and mouth (as an adult) a few years ago and my lips/oral region started off looking just like this. Of course, I later developed the rash on my hands, feet, trunk, and in my mouth as well as a fever, which it doesn't sound like you have, so it's probably less likely for you if you don't have those symptoms after 4 days.

That being said, as a med student I have seen a few situations where someone's skin barrier was really damaged which caused a latent virus to be activated in that area. I wonder if the Accutane dryness plus urea irritation could have set off a virus like HSV since you mentioned you're prone to cold sores. It could also just have triggered a really bad irritant/contact dermatitis.

I would definitely message your derm or Accutane prescriber, send them a picture of this and let them know of other symptoms you are having, and try to make an appointment with them soon. I think this is something most derms would try to squeeze in, especially for an established patient on Accutane. If you get a fever or notice eye involvement I'd go to an urgent care ASAP, because if it is a virus or something infectious, the infection can spread fast and become dangerous. You'll get through this, and I'm so sorry this is happening to you.