I keep feeling these weird thumps in the top right side of my stomach when I stretch. It startles me…

I keep feeling these weird thumps in the top right side of my stomach when I stretch. It startles me so bad that I yell. It has only happened 4 times in the last 2 weeks. I didn't experience this with the other 3. It can't be the baby because it shouldn't even be that high yet! Has anyone else felt that before?