Periodic bouts of diarrhea, burping

It happens the same way every time. It starts out with excessive, unusual burps (possibly sulfuric, though I'm not to familiar with those, since these nothing like regular food burps). Then begins the bouts of diarrhea, which don't usually last longer than 24 hours. My stools become more liquid over time (possibly because I switch to drinking clear liquids?).

This whole process happened 3 times in 4 weeks a few months ago. I thought it was food poisoning at first, and then on the third time I went to see my doctor for fear of it being an intestinal parasite (I was in Namibia for 7 weeks last summer). He wanted to do a stool sample, but after that appointment I stopped getting sick. And then it hit me again today. I had stopped bringing the container with me so I couldn't collect it at the time. Now I fear I won't go again until tonight or tomorrow, when the clinic is closed.

Any ideas as to what I have or what to do?

[jescapism]

By the way, I'm a young adult female and I can't seem to link these bouts to any particular foods.