It sounds like a rotator cuff
pathology. The rotator cuff is a group of muscles around your shoulder which can get inflamed (it is NOT an infection) and diseased. It is also very common to get the bursa (lining over the tendon) to become thickened and inflamed too, producing an impingement syndrome
Steroid injections (like cortisone
) can cure some cases but many can recur after a few weeks or months. If it continues to trouble you, you should see a shoulder specialist where an shoulder Ultrasound
can be arranged to assess the shoulder.