Rt Shoulder And Neck Pain,throbbing While Resting Or Active,pain Irradiates

rt shoulder and neck pain,throbbing while resting or active,pain irradiates down rt arm into elbow ..painful to bend elbow into 90 degrees and pronate hand..also painful thickening in rt muscle from inner to outer mid humerus area..no previous injury..also weakness when trying to lift certain objects according to weight of object,but no problem lifting arm forward or overhead..can you help narrow the possibilities? YYYY@YYYY thank you