My stomach has been having little weird pains around bottom. and just few weeks ago i had acid reflux. when i try to do sit ups (at least 10min) it was hurting for couple minutes.do that have to deal with that this is this something else?

Stretch exercises.: I would suggest that you warm up by stretching both before and after completion of your exercise. I would consider that you do crunchs and do them in 3 different heel positions from your butt. I would do those in sets of 10 in each position. I would consider that you would do the exercise about 4 hours at least after eating. I would follow up with your primary physician.