K.B.
Gallbladder pain is really intense. I used to have gallbladder issues - specifically, gall stones and when one happened to be passing through the bile duct that empties into the small intestine, the pain was enough to make me want to die. Seriously, it was the worst pain imaginable. Like passing a kidney stone, but a different location. Centered in my upper abdomen, but radiating around to my back. It would be triggered by eating any foods or a meal that was greasy, fried, or high in fat. It would last from 10 to 20 minutes, than subside on its own. Sometimes I ended up vomiting and then the pain was gone. Getting my gall bladder removed fixed that permanently. The doctor actually saved the gall stones they found in a container and showed them to me. They were only slightly bigger than grains of sand - they were so tiny, and I couldn't believe something so small could cause so much pain.
However, I can't comment if you are feeling a bump like a marble. I wouldn't think that that would be a sign of constipation - having hard irregular stools and trouble passing them is constipation. Gas that builds up in any area for any reason will cause pain too. Or you could have the beginnings of a stomach ulcer or acid reflux.
Bottom line? Go to your doctor and start having some diagnostics done to get to the bottom of it.