Zantac is safe to take one a day. I use dot the first 4 months. Now it's back and I'm using them again.
The chest pain could be from the heartburn, actually. I mostly take tums for heartburn, but you don't want to take too much. If it's really bad, talk to your doctor about something to reduce acid production (tums just deals with the acid once it's produced). I can't remember what it's called, but you take one pill twice a day. I took it for awhile, it's safe for pregnancy.