I have a large gallstone, but only seem to get pain in the night & not in the day after eating. could it be something else?

Yes: Pain associated with gallstones, termed biliary colic, is most typically in the upper right side of the abdomen and usually occurs after eating (fatty meals are most pronounced). This is because the gallbladder contracts in response to a meal in order to empty it's contents into the bowel to aid in digestion. Gallstones can intermittently obstruct this emptying.