2 squeezed lemons mixed with an equal amount of olive oil will be much gentler than the Epsom Salts if you are concerned about it. Take it on an empty stomach, lie on your right side with a heating pad. Pulling your knees up like the fetal position will open up the ducts to let any stones through. Take it before you go to bed and you should get relief from the gallbladder pain. I have done many Epsom Salt flushes and it does get rid of the pain within an hour. It is rather rough on the digestive tract though and you will need to be near a toilet for a day or two. Either one will be helpful.
PS I have found even 1TBSP of epsom mixed with 8oz warm water and some juice for flavor will relieve a GB attack within an hour or less.