spasms, bursts in stomach...vomit from pain. pls help

hi, my mother has been experiencing major stomach problems for a couple years. she is 50 yrs old. she was diagnosed w/ colitis in her late 20's. she also had an ovary removed. but in the past few years...every 6 weeks or so(sometimes 2 months) she gets these INTENSE pains in her stomach. she calls them spasms...and its like pressure that needs to burst. it lasts about a minute or two. and then she'll get it anywhere from 10 minutes later (at the height of it) or could be and hour or two later (at the beginning or end (first or last day)..It lasts 3 days. the pain is SO intense that she vomits. like i said, it only lasts 3 days...and the next day she is completely wiped out from throwing up all day and night sleeping. does anyone have any idea what this is? she has gone to the doctor a million times, had all tests done...they dont know what it is. if anyone has experienced this or knows anyone who has, please write to me and give me some info on what it is or how to treat it. please help!