A few weeks ago I woke up with yellow crust on the corner of my lips and it went away in 2 days, and today I woke up and it's in the exact same spot again except a little more then before. It doesn't hurt or itch, it feels like my lips are very very dry. I don't smoke, I have grandmal seizures and my medication is phenytoin and kepra but I didn't read anywhere that would be a side effect so I'm worried this could be a STD or something.