Azithromycin
"I am eight and a half months pregnant and I took a 2 pill dose today.  About an hour or two later I woke up with intense abdominal pain. At first I just thought I had to use the bathroom and when that didn't help I started to cry. And pray. I recently felt some diarrhea so I handled that and then took a hot shower. it's about 3 or 4 hours since I took the pills and the pain has subsided a little."