Hi I Have A Burning Sensation, On The Outside Of

Hi i have a burning sensation, on the outside of the stomach, mainly on my right side. Mainly where i have my stretchmarks. It can be as sharp as a knife stabbing me or like a burn you get from burning yourself with hot water. Sometimes it is acceptable but most times it hurts a lot, comes quick and takes at least 10 min to go away. Clothing can irritate it or lotions. I believe it is mainly since i started to increase my excersice routine. What could it be?