No, you haven't permanently damaged your stomach.  Gastric upset from
antibiotics is extremely common.
    Call your physician--he/she may be able to substitute an antibiotic
that will be less irritating.

Steve

Hello,
I'm not a doctor. It's my guess that your stomach will heal on it's own in
couple of weeks (or less). If you still have the stomach problems at the
end of a two week period of time, you need to see your doctor. There is a
test that the doctor can do that will determine whether or not your
stomach has been damaged or if you have an ulcer. The test involves
drinking a terrible tasting solution and standing in front of an X-Ray
machine. You might consider taking Pepcid or some other brand of antacid
during those two weeks.
Jason