Aside from muscular issues, this could also be due to gall bladder stones which usually presents with sudden and rapidly intensifying pain in the upper right portion or center of the abdomen
just below the breastbone, back pain
between the shoulder blades or pain in
the right shoulder. The pain usually lasts for several minutes to a few hours. You may benefit from additional diagnostic tests including imaging studies such as ultrasound or CT scan .Take care and do keep us posted.