What Causes Tenderness And Severe Pain In Abdomen Post Gallbladder Removal?

I have a father that recently had his gall bladder removed. It was back in September. He now has severe pain in his left side just above his abdomen. The gall bladder was badly inflamed which was the reason for its removal. The problem is that the pain is worse than ever. He has had blood work, ct scans, x-rays, and even an mri has been performed. All come back okay. Hes been checked for cancer. GI s have also been ran with no signs of any problems. Constipation has been an issue along with this. He is almost unable to get up and down and move around. He is pretty much disabled at this point. He also has a knot that has come up on that same left side. Its about 2 to 2 and half inches in diameter and it protrudes from the surface of the skin 1/2 inch or so. Its very tender to the touch and hurts severely. The knot doesn t show up on any of the results of the aforementioned tests. Can you please help? We have no idea what to do next or who to see. The doctor that performed the surgery comes highly recommended, but seems to be out of ideas himself. The PCP also is puzzled. Please if you have any ideas about what we could do, get back with us. We are very worried at this point. Thank you in advance for anything you might be able to do.