I went swimming & my arm was forced backwards by a wave i felt pain as my shoulder cracked, 3 weeks i still feel pain & cant sleep on my shoulder.

See your physician: The persistent symptoms are concerning - see your physician. Hyperextension of the shoulder involves the rotator cuff muscles and the shoulder joint, also known as the glenohumeral joint. Injuries can include tears of the muscles and tendons and inflammation of the tendons. http://www.nlm.nih.gov/medlineplus/shoulderinjuriesanddisorders.html