I get some condition happening where the muscle wall behind the boobs seizes..........the pain is RIGHT under my boobs. But it's nothing serious - feels like a heart attack but it's just muscular.
I had this too during my pregnancy. It started around 7 months and the pain was horrendous. I mentioned it to my Dr several times but he always reassured me it was just muscular and would get better one the baby came. It did get better after the baby came but my DS is now 2 and it still bugs me on occasion if I bend the wrong way.

I would definitely get it checked out though to make sure it isn't anything serious. it's not a waste of time if you get to put your mind at ease.