I had my gallbladder removed in '93 and immediately started having constant diarrhea. I would mention it to my GP and she acted like it was normal after having it removed. In fact, research says that up to 10% of people will suffer from diarrhea after this operation. Both my aunt and sister suffer the same.
However, with me, I think some of it was symptoms of UC. It was always full of mucous and occasionally, lots and lots of blood. Not until December of 2005 did I start showing more severe signs which resulted in my diagnosis. I suffered from constant diarrhea for 12 years before being diagnosed.
Two years ago, I found a webpage, which I can no longer find, that had a long list of illnesses, diseases, etc that are directly linked to each other. Having your gallbladder removed can be directly linked to a diagnosis of UC down the road. I don't remember the stats but it was a "lightbulb moment" for me when I read that. Asthma is another disease linked to UC, which I also have, although it is well controlled. I really wish I could find this webpage!!! It was full of information and most of it made so much sense to me.
In the meantime, can you try cholestyramine to control the diarrhea? It really works for me. It is a drug used to reduce cholesterol but it is also an antidiarrheal. It binds to the bile salts in your system and helps tremendously in controlling diarrhea. Having UC and then topping that off with diarrhea caused by having your gallbladder removed is a double whammy. I can sympathize.