Severe right upper stomach pain, found out its gall stones. seeing surgeon, heard people gain weight after removing gall bladder, true?

Not true: It is not true. If you stay active and watch out your diet, you should be fine .

Cholecystectomy: Well, there are some publications in literature regarding weight gain after Gallbladder surgery but it seems 1/3 of people who need Cholecystectomy are obese to begin with, the studies showed that people who maintain a low fat diet and exercise don't gain weight in comparison to the people who did not. Therefore the main point here is to exercise regularly and maintain a good balanced diet.