Hello! Excuse yourself, go to the bathroom or outside and let it out, don't hold it in, do you have regular bowel movents, you might be contipated, check with the dr because I am not one myself, you might have a pulled muscle, it could be a lot of things but your 1st step is going to the dr if you cannot figure out or treat your own situations.
Good luck!
Keep us posted on what you find out!