I had a mammogram and i am sore in my peck muscle and under my arm. i feel as though i feel movement in my peck area. ?

B/c of Mammogram: Mammography requires pressing the breast hardly against the scanning apparatus. It can cause pain in the pectoralis muscle and discomfort under the arm b/c of lymphatic drainage of breast includes the under arm area. Compression of mammary glands and ducts may make u feel that the peck area is moving. Involvement of pectoral muscles , may also make u feel that way.

It is possible: that the positioning and compression requirements of mammography caused some temporary soreness. If it doesn't improve in a few days, talk to your doc.