Needing Advice

Sometimes it looks like my baby’s stomach is bulging on one side or the other and it switches back and forth when he flexes or moves around. It doesn’t happen all the time, mainly after he eats and/or I am changing his diaper. I just figured he was learning how to move around his body. He’s 7 weeks and acts normally (not in pain of anything) Is this normal? Just wanting advice or to see if others do this before I give a call to his pediatrician.