I'm Having A Colonoscopy And Upper GI Done In The

I'm having a colonoscopy and upper GI done in the morning I have not had solid food since Friday today my prep of two bottles of magnesium citrate four hours apart than two hours later I have to take three laxatives ducolax... the magnesium citrate is making my stomach hurt and I'm starting to feel weak ... What are the side effects of magnesium citrate and isn't this a bit too much for what I'm having to have done