I'm 3 weeks post op and I was the same way. The shakes I had before surgery, still tasted fine, but I just didn't want them. So I brought some decaffenated tea and used 3-4 packets of splenda. Drinking it hot really helped.
I usually have a cup of tea every morning now. I'm not a great pill taker, so I didn't want to have to take anything else. The tea really works for me.
Now when I don't want something, I just don't eat it. My doctor told me to stop thinking that I have to get all those shakes in one day. Our stomachs are really small and can't hold all of it.
Don't force yourself to do it. Find another source for the protein. Take it slow. Take your vitamins.