@SandyT I'm having a gastric sleeve on May 6 as well! Glad to read about others' experiences here, helps me feel like I'm not on my own.
I started my protein shake diet a couple days early on 4/19, and it has been rough so far (extreme fatigue, headaches, brain fog, and bloating). A few people have told me it usually gets better after 3-5 days, and I really hope that's the case!