Hi , My Wife Is 20 Weeks Pregnant And Has

Hi , my wife is 20 weeks pregnant and has been experiencing side pain ,starting from her bottom rib on right side to the waist Line. Pain strike suddenly , mostly at night and last 15 to 20 mins at a time. Docs have checked for UTI and Gall bladder , both clear which is good. However what else could cause such severe blinding pain?