I have a severe pain in my shoulder and a weak, tingling left arm. what could be wrong?

Evaluation Needed: After a proper history, physical exam and any necessary imaging (x-ray/mri) is obtained and reviewed a sufficient diagnosis can be made. Treatment may include but is not limited to ice, heat, massage, nsaid's, physical therapy, chiropractic, orthopedist, and pain management.

Perhaps 2 issues: Not unique to have trauma to shoulder, with possible rotator cuff tear, and associated injury to the brachial plexus. But severe abrupt non-traumatic shoulder pain associated with numbness and/or weakness in the arm may be due to brachial plexitis (parsonage-turner syndrome), and should be managed with steroids. Last caveat, left arm can be associated with a cardiac issue. Get all checked out.