Could it be gallbladder cancer?

Sounds like just gallstones, consider getting the gallbladder removed. Gallstones can give horrendous pain and over 99% of the time cancer isn't the issue its the gallstones themselves.

Does not sound like cancer, sounds like gallstones. Gallstones attack can be extremely painful. I found it worse than childbirth.

There is no reason to assume it is cancer.  Gallstones are quite variable.  The size of the gallstone or the number of them will not tell you how much pain it will cause.  It depends on its position and whether it is blocking the exit, among other things.  See the doctor again and see whether s/he has anything new to say.  

I don't see any signs of cancer. Just worsening gallstones. So get it out already. They can usually do it via laparoscopic and it's not a big production. I didn't spend a single night in the hospital, that's how easy it was.

Take your attorney with you and meet with the doctor.  Make it clear you are looking for a 7 figure settlement.