ever since I took zithromax a month ago, I haven't felt well. Upset stomach, loose stool,etc.. I have GERD and a hiatal hernia and I am prone to chest pains, etc. Have had many tests and they say there is nothing wrong with my heart. However, ever since I took the meds, I have been having back, shoulder, arm, stomach and chest discomfort. The pain travels and is short lived, and sometimes it gets worse when sitting.