It's normal. She will start to pee more soon and she'll want to eat and drink. Remember that she had her reproductive system pulled out yesterday. It's a major abdominal surgery that is comparable to a hysterectomy. It takes time.
You did a good thing for her.
Pain meds should always be given post spay. Antibiotics are optional. Some vets think they are needed and some don't.
My girl was really down for a few days after her spay and she ended up coming out of it just fine.