What Causes Pain Between Shoulder Blades?

i have pain in my back between my shoulders blades the pain radiates to my rib cages and then to the front . at this point i have to lie down and relax or pain gets worse (it can get pretty bad) i can feel pain radiating down towards stomach causing cramps or spasms and then downwards to my uterus moving its way towards the lower back. at this point the pain eases. unfortunately my pain continues this is day two the same process follows each time. after each episode i feel better but i can feel each episode coming back again. starting in my back. please help.