Hey if you have acne mostly around your mouth that sounds like it could be perioral dermatitis. If you used a fluoride toothpaste, you could be suffering from a sensitivity. Get a new toothpaste, something mild and natural, like Burt's Bees or something, without fluoride in it.
Do that for a few weeks. Yes, weeks, and I would also leave it alone - try not to apply too much stuff to it, if it really is perioral dermatitis topicals could be making it worse.
Oooh and I just read that you're on accutane. Well, might as well change your toothpaste anyway. Accutane has the potential to be horrifically destructive. It's used in some chemotherapies because it destroys stem cells in the gut. I hope you don't suffer side effects