Any antibiotic kills your good bacteria as well as your bad, so you could be sensitive to all antibiotics (I am), but some antibiotics are much stronger than others, thereby causing a worse reaction for you .

Once you stop the antibiotic, find a good probiotic (like acidophilus, etc) supplement with a high live count. Yogurt usually has some "live and active cultures," but you are going to need more than what a tiny cup of yogurt can provide in one sitting. Check out the refrigerator section of a health food store (their live count stays higher if refrigerated), or if you have a Whole Foods near you...either should provide several options. I know Solgar is one brand that makes a few such supplements.

If you feel like your stomach is too upset to take this antibiotic, definitely call your dr and see if you can try something else, FOR SURE. Regardless, I would still find a good replacement supplement for afterwards, your insides will thank you!