Lower Rib Area Pain. Done CT Scan, PET Scan And Ultrasound. Is It Related To Gallbladder?

i have had a pain that can come and go but the pain is usually in consistently the same, never terrible enough to stop doing anything that I am doing, but it always comes back. it seems to wrap around my lower right rib and can end up on my right side of my back. When i stand up and move around it goes away, but sitting usually makes it worse. pushing on the area gives me no pain. I have had a ct scan, and ultrasound, but nothing is showing up. of course, i worry it is the most terrible thing, like a large tumor! I have had this for well over a year and 1/2. I have been seen by a doctor. No bowel problems either. I thought it was my gall bladder, but the ct scan revealed nothing. I even had a PET Scan a year ago June, and nothing. I'm feeling paranoid because it's constantly on my mind. Any ideas?