Virus 12 days post op

Ok, so 2 hours after I had a glass of milk last night I had cramps and fever. I’ve been on the pot every 1/2 hour ever since. I’m now pooping dust but still have diarrhea cramps. Fever has gone up and down. I was doing great with liquid intake up until last night but so turned off by drinking much except water. Should I go get an iv bag for hydration? How do you know you’re dehydrated?
I’m going to call dr but I know some of you have gone back to get fluids... what were you feeling to make you think you were dehydrated? Thanks guys!