Uterus pulling on ribs?

Whenever I sit down, or lie on either side, I have the strong sensation that my uterus is pulling (hard) on my ribs. It hurts the front and back of my chest, and affects how much air I feel I'm getting. Everything  just feels so darned tight inside - as if something needs to stretch, but won't. Anyone else experiencing the same? Any suggested remedies? Only thing that helps so far is laying on my back, but I know I'm not supposed to do that!