I have a friend who's stomach did that, looked like she was pregnant all in one day but wasnt obviously and it was kidney related.

-H. Pylori or any other infections, or conversely a depletion of "good" bacteria"
-Gastroparesis (stomach not working - major fullness)
-liver problems (light-colored stools is not good if consistent)

I would give probiotics a try 1st thing. GNC has one called the enzymic whole body cleanse but there are several out there. Once they are opened make sure you keep them refrigerated.

antibiotics are if it's an infection.