The fact is that there are a LOT of possible side effects after the removal of your gallbladder (most stemming from either (a) problems with the surgery, or (b) another underlying condition like SOD). However, by far the most common is diarrhea (usually after eating fatty meals). For the record, however, the gallbladder doesn't help digest anything. The BILE the gallbladder holds is pumped out into the small intestine whenever there's fat there so that it can be digested. Since you no longer have a gallbladder, bile is now dumped directly from your liver into your small intestine (hence the diarrhea after meals: the liver will dump a bunch of bile. The gallbladder was what helped keep things in check and dumped the bile out slowly).
As for gaining weight, the only reason people do is because now that they don't have a gallbladder they no longer feel pain or discomfort when eating foods they shouldn't in the first place (like fatty or fried foods, and alcohol) so they start eating a lot of them.
For the record, however, whether you had gallstones or whether there was something else (dyskinesia, polyps, etc) will usually determine what type of possible issues may affect you in the future relating to that region of your body. Recommendation: do your research and take extra care with your diet, and you'll probably be OK.
Well you have had it removed now but go online and Put Gall Bladder Removal in, you will find a lot of information there.