Hard Painful Knot, Come And Goes Under Rib Cage. Get Relaxed By Massaging. What Is It?

Thank you. I am 50 years old. For the past 8-9 months, I have started having a hard painful knot right under my left ribcage off and on. Happens when I rise from a lying down position and getting up from a relaxed sitting position, and when I had episode of vomiting recently. Is almost the size of fist, very painful (feels like bad leg cramp ) and I have to massage it down and relax to make it go away. Remains very tender there for several days afterwards. It happened a few months ago and was so painful I went to the ER for it. By the time I was seen, the knot had relaxed, but area remained very sore. They gave me a pain shot and then I had a CT scan . The doctor said I had a bladder infection and a cyst on my left kidney, but no active infection in that area. I truly don t think the bladder thing was related (I had no urinary problems) and still this painful knot comes and goes. What could it be?