What Causes Nausea?

My heart feels like it's being sliced through. I'm 16 and not overweight. It happens once every month or so for a few days and I get nausea right after. It just happens randomly then goes away quickly and leaves a dull pain for five or so minutes. It doesn't feel like its being squeezed but rather like someone sticks a knife and slices through it quickly then the pain is gone. I've also noticed it goes away instantly if I squeeze my left breast or push on my ribcage.