Some antibiotics are really hard on your stomach. Usually in the side effects area, they will tell you if you experience diarrhea, to consult your doctor. My mother took an antibiotic called Levaquin and it gave her extreme diarrhea. I called her doctor and he changed the prescription immediately and told her to take Imodium. They don't tell you how many bad side effects antibiotics can have, but read the inserts. Good luck.

Antiobiotics can cause an imbalance of the good/bad bacteria (flora) in our intestines. Are you eating yogurt or taking any probiotics? What was your first antiobiotic for the sinus infection.....my stomach problems started w/antiobiotics and Levaquin was one of them.