Of course, garlic can cause gallbladder distress because garlic is a cholagogue = a food/herb that increases the release and flow of bile. And some say it's a choloretic, too = increases production/amount of bile.
Increased bile flow through a clogged liver/gallbladder can = liver/gb pain & distress.
Killing parasites + increased bile flow through an already clogged liver/gallbladder = more carcasses to clog up the works and more distress.
Doing coffee enemas should give you great relief (and should always, imo, be done when killing liver flukes as to ensure the dead carcasses aren't rotting in your liver...as well as clogging up the works). A castor oil pack is likely to be a relief, too.