I started an antibiotic 10 days ago or a sinus infection. A couple days after I started it my stomach has been a wreck. Gas, bloating, weird bowel movements, feeling like I'm going to have diarrhea but not, and nausea. I have never had these issues before on antibiotics. I keep thinking I'm coming down with a bug which kicks up my anxiety even more, which in turn isn't helping the bowel issues. What the heck s causing this? I haven't had IBS in years. The only thing I've had very occasionally is diarrhea postpartum on and off for 5 months, which I believe is hormonal. Can antibiotics really cause this upset? I've been off of them for 3 days now ad still feel these issues. Help.