Hello there, I had the same problem plus along with it very embarrassing and uncomfortable gas. I had to find a protein powder that I liked the taste of and
one that would not cause............well you know :->). Slim fast did not agree with
my stomach at all. I bought something called "Pure protein protein" powder
at Target. It worked well for me. I don't know where in the country you live
but I think the good news is that most stores will accept returns of even open
items if you have a receipt. So I think maybe you can try different kinds of
powders (return what does not work for you) until you find one that suits you.
I will probably be starting my pre-surgery diet in a few week and it sounds like
you will be too. I hope this works for you. Best of luck to all of us.