Does anyone else get one every time they start a new workout routine?

Third time now that I have started running again after a break and within a week there is a sore on my bottom lip. I thought exercise was supposed to help with stress, not set these things off. Is it the sun on the runs, the sweat, or just my body freaking out about the change, does anyone know? Kind of tempted to keep going anyway and see if it settles down once I am used to it.