Great suggestions from all above. Mactan23, read up on MSG and it's 13 other names. MSG causes neurological problems along with digestive problems. Start eating unprocessed foods....no chemicals! Stop microwaving...check out the dangers of microwaving on the web.
It is very common (and almost expected) for those who suffer anxiety to experience digestive issues as well, myself included. Undigested food, stomach acid, bloating, gas, the list goes on. I stopped taking prescription medications for my anxiety/depression/panic attacks as the side effects were handing me all sorts of extra problems and I felt like I was being flooded with too many toxins and chemicals from them. In the end, the meds never cure the problem anyways. I know it is easier said than done and certainly frustrating to think of all the money and time you've spent on these meds, but this is why I am such a strong advocate on alternative methods for anxiety and phobias. They can actually cure the problem, instead of masking it.
Do some research on hypnotherapy, naturopathy and kinesiology before confusing your body any more meds!
I wonder if the zithromax killed not only the bad bacteria in your body but also the good which could cause digestive issues. Try some Acidophilus. I would also like to add that I take adderall for ADD and I started off with Ritalin. I have more acid then I used to have without so, it could also be a side effect of the Ritalin as well.
Flagyl has some antiinflammatory properties, for unknown reasons, but it also kills off your beneficial flora in your intestinal tract. Try adding some bifido bacteria focused probiotics to replenish what the flagyl has killed and see if that helps. Many meds also can cause stomach upset, and yes, stress can affect the gastro tract in a couple of ways, one by creating nervous stomach, and two by affecting digestion -- most of us with anxiety don't chew out food slowly and our stress impedes full digestion. Digestive enzymes can be very helpful with this, as can aloe juice and DGL (a form of licorice). Diet can also be responsible, with the usual culprits -- wrong kind of fats, too much white flour, not enough fiber, etc.