If you've never had a positive herpes test, and it's an IgG blood test, then you don't have herpes. You should start looking at allergies (food, drink, lip balm, toothpaste, etc), and see if that comes up with anything for the mouth symptoms.
Leg pain can be caused by many things, included a pinched or entrapped nerve, a pulled muscle, etc. You don't describe it, so I can't pinpoint it more, but continue to work with your doctor, and perhaps ask to see an ortho or neuro doc to help with that.