What Causes Tingling, Numbness And Burning Sensation On Lips?

I am a 46 year old woman whom has had a double bypass and a grastric bypass. This past week I started having tingling, slight numbness and a light burning sensation on the left side of my bottom lip. It was off and on at first, but now for the past three days it has been continuous. I went to the doctor today and he couldn't figure it out and is treating me with steriods. If you can give me any answers at all it would be greatly appreaciated.