I had a similar pain but in my second trimester. It was a little to the left of middle. OB said it was stretching and to take it easy. I didn't have the pain all the time though just when I had to bend down for something or I rolled over in bed. Are you by any chance wearing an underwire bra still? If so maybe change to one without the underwire. I hope that you get over the pain soon. If you continue in pain I would probably go and visit your GP.