Nausea, dirarrhea between periods - not pregnant

For the last 2 months I have been sick to my stomach, diarrhea with severe cramps, fatigue, burping, and some acid reflux. It seems to start about a week after my period and goes away about the time I ovulate. I'm not pegnant. I am over weight. I just had an abdominal ultra sound this morning which showed. No gall stones. I'll get the full report in a few days. Any other possibilities for my symptoms? I would like to have another baby soon. I'm 40.