I occasionally get gallbladder attacks but they seem to mostly occur when i'm on my period. i do have enormous uterine fibroids for which i'm scheduled to have a hysterectomy, but i'm not sure why my period would impact the passing of the gallstones?

Menstruation does not have an effect on the passing of gallstones. Passing a gallstone occurs when the gallbladder contracts, and when a stone exceeds the diameter of the cystic duct (the exit of bile from the gallbladder) , the pain is proportional to the disparity in size b/t the stone and the cystic duct. Get a second opinion about a hysterectomy, b/c there are other options available.