My cat won't eat and drink after spay surgery

My cat (girl) had spay surgery 3 days ago. And the day after her spay, she started to having a fever and did not eat and drink. I took her to the vet and they gave my cat some antibiotics said this would make her feel better. Today she still refuse to eat and drink any normal food. She only eat 3 cat treat this morning and wont eat the normal dry food and canned food she used to eat. Is this serious and what should I do?  (she just keep sleeping all day and not seems to walk)

She's probably still sore, but usually they start eating OK after a couple of days.  Try some very smelly cat food, or even tuna.  It's very important that she eat something, or her liver can be damaged.
 

But why she won't drink water either? I am afraid that she will be dehydrated.  She just ate three cat tuna treats. 

You can check to see if she's dehydrated by lifting the scruff of her neck - it should ping back and be very elastic.  However as you are worried I think you should be ringing your vets again.