Dear Lisa,
Definitely KEEP DRINKING enough, even if you don't feel like it. Fruit juices, soups, etc. can give you some nourishment along with the fluids. If you have no appetite, keep stuff nearby that you might like and nibble and sip whenever you can. Even a bite or this or that, a few spoons of yogurt, whatever, all adds up. You have been through a major surgery, so make sure you keep well hydrated and nourished so you can heal. Don't worry about wasting food for now. Better to have one bite of a sandwhich and dump the rest than not eat at all. Get your favorite ice cream, even if you only feel like a spoonful or two.
Fr. Pat