Throwing Up and Freaking Out!!!

I am 11 days till surgery and they just started me on my 5 meal replacements a day (800 calorie diet). Only problem is, I'm throwing up the shakes in the morning. I cannot drink milk in the morning for this reason. It's not a lactose thing but a consistency thing. I am not mixing the drinks with anything but water but it reminds me of milk. Tried taking crystal light and mixing with that.....bad choice. I had to dilute the shake down to pretty much nothing. I am drinking my shake right now and gagging every sip. It has gotten better now that I put in a ton of extra water. The Bariatric Advantage drink I have right now is slimy. When I dilute it, that helps but its the initial first taste that makes me gag. The after taste isn't as bad. Any suggestions what i could do?