I have a painful sore on the corner of my mouth. Can I send a picture?

Angular chelitis. You can send a picture but it will not open in this forum. The most common mouth-corner sore is called angular chelitis, and it responds well to B-comples vitamins. See your Dentist for an accurate diagnosis and appropriate treatment plan.
Sore. Probably perleche. Apply cortisone cream to area twice a day for one week.