Do you have big boobs? I only ask (not cause I'm a weirdo ) cause particularly when I'm pregnant and my boobs get even bigger, I get some condition happening where the muscle wall behind the boobs seizes? It freaked me out when I was pg with #1 and had to go to emergency and get an ECG, but that's what it turned out to be, and my physio has since confirmed it. It's kind of an extra weight thing, and kind of an inactivity thing (cause it's not like you're jumping them around too much when pregnant, iykwim) And the pain is RIGHT under my boobs. But it's nothing serious - feels like a heart attack , but it's just muscular.

But to be safe, get it checked out - at least you'll rest a bit easier x