I am a 41 yr. old female in good health generally. (3 kids, 5 5 , 127 lbs.)I have a lump in what I think is my AC joint on my right side. It is visible and probably the size of a small grape. It is painful, but bearable. There is a constant pain there, but lifting and rolling my shoulder back definitely makes it worse. Rolling my shoulders back has always made them pop, but did not use to cause pain. It has been bothering me for a couple of months now and is getting worse. Is this arthritis? A bone spur? I am suspecting arthritis since I have mild guttate psoriasis...I returned to work last year and have been carrying a very heavy bag on this right shoulder... so originally thought the weight was bothering the joint. I noticed the lump last month. Your comments are much appreciated.