It could be two things... first you may have a problem with the Protein you are drinking. whey caused me all kinds of problems.. even lactose free protein like Isopure.
Second, it could be all the artificial sweeteners. I usually drink a lot of diet coke and things like that (at least I did pre-op) but not nearly as much as I did on the liquids. My dietician took me off of whey and anything artificially colored or sweetened. I'm eating lots of chicken broth!!!