I have a really bad chest pain in-between my chest just under my breast. I've had it for three days & it feels like it's getting worse. When I breath it hurts. I tried to sleep it off but that didn't help. Last night it was so bad it had me throwing up. What can it be?

I would ask you to seek medical assistance. We do not diagnose on AMHD as diagnosis cannot be accomplished on the internet,

If it's on your right side, I would think it could easily be your gallbladder.
It doesn't matter - why aren't you seeing a doctor, clinic, preferably not the ER but go to the ER if you have no where else to go?
If it's your gallbladder on the right, you must see a doctor.
If it's your heart on the left, you must see a doctor.
If it's an ulcer in your stomach right or left, you must see a doctor.
If it's something else... it could be serious or not, you won't know!