Hello and welcome to the forum. We appreciate your question. The best thing to do is to have this looked at by a doctor to diagnose. However, things that come to mind are an allergic reaction. You mention chapstick. Could you be reacting to this? Your doctor could check your vitamin levels as they can cause issues like this. Dehydration adds to it. There is also the possibility of herpes simplex 1 which is oral herpes. Approximately 80% of the population has this including many who got it as children. Here's information on that. https://www.webmd.com/a-to-z-guides/oral-herpes#1 And while it is not a terrible risk, you would also want to rule out any type of skin cancer. So, if this is continuing and been going on, it is time to get checked by your doctor.