After i had DD i kept getting sharp pains in the middle of my chest right where my bra was and they were VERY painful, they didn't ease and one day i started to hyperventilate from the pain.. turns out i had gallstones.. OUCH!
I seriously thought it's the kind of pain a heart attack would feel like.

They say a lot of pregnant women get it as they increase the amount of dairy they have, it might be something to look at. Might started out a low tolerable on and off pain but when a a stone got stuck.. OMG.
Hope it's nothing serious...