I just woke up from a nap and had a stabbing pain on the right side of my chest under my breast. When I move my right arm the pain gets extremely bad until I just lay it down. I am also getting a pain in the back of my right arm. Im 20 weeks pregnant and worried.
In most probability the pain which would increase or decrease with SRM movement is local in origin and NOT heart, so be reassured.  I believe the kind of pain you describe and the circumstances in which it has occurred, is mostly probably due to a nerve compression as a result of position you took during the nap.  It would resolve in a day max, some warm compress will help, may take a single tab of paracetamol 650 mg SOS, which is perfectly safe in pregnancy.  Regards Chat Doctor.