A really simple thing you can try right now is probiotics. Probiotics are good bacteria which populate your gut and help you break down food. Certain illnesses, bad water, antibiotics, etc. can upset the balance of good bacteria and bad bacteria in your guts. If you get too much bad bacteria, your guts don't function properly and diarrhea, cramping and stinky gas are all symptoms. (In fact, stinky gas is almost always caused by a bacteria problem.)
I would suggest getting Culturelle. You can find it with the other bowel products in any chain drug store. It's what I've been using to straighten out my guts since I got into, I think, bad water last week. My GI's nurse practitioner suggested it and said she had used it while in Mexico to avoid Montezuma's revenge (she was the only one in her group who didn't get it, so I would say it worked!). I feel like it's stronger than the Digestive Advantage (which I can't take because it has sugar alcohols in it, which give me even wose D and cramps).
In addition, you can also eat yogurt and/or drink milk with acidophilus in it. Both have small amounts of probiotics and are good for daily maintenance (however, to start with, be sure and take the pills, because it sounds like you need a strong dose). If the Culturelle gives you more gas (probiotics can do that until you get used to them, just like fiber), take it at night, before bed. That's what I've done in the past and so I end up sleeping through most of the gas.
If you take antibiotics in the future, be sure and take some probiotics with them to avoid this same sort of situation. I never take antibiotics without probitoics anymore, because the probiotics keep me from having diarrhea as a side-effect of the antibiotics.
If you don't notice any improvement at all in two weeks (it may take a month to get totally corrected), then you're going to have to see a doctor. You should be going home for the summer in a couple of months, right? See one then. Be sure and see a GI doctor. Even if the probiotics don't work, it doesn't necessarily mean that you don't have a bad bacteria (or bacterial overgrowth) problem; some bad bacterias are just so rooted in your guts that it takes antibiotics to wipe them out and then you have to start over again with the probiotics. A GI doctor can prescribe a test that measures the gases that you exhale; if you exhale gases which are not a part of a normal human's respiration, then they know you've got bad bactiera in there, creating unnatural gasses. If it's not a bacteria problem, a GI doctor can at least prescribe an anti-spasmodic, which should take care of the cramping and hopefully reduce or even eliminate the diarrhea.