My 5 year old cat lily is lethargic

My 5 year old car lily is lethargic, had been for 3 days now, I took her to the vets yesterday, she had a High temp, not eating, drinking, but not very much. Normally very loving and playful. Was projectile vomiting too. The vet gave her 2 injections, an anti sickness, and an anti biotic. And give me anti biotics to take home. She had 2 tablets today, but us still very lethargic and is hiding in her pet carrier under the stairs. I am worried sick. How long do I wait before taking her back to the vet? Should I of seen some improvement by now? She was seen at 7pm on the 13-12-13, has had 2 anti biotics today 14-12-13. I am just going to bed at 12.15am 15-12-13, but am worried to bits. Sorry if I come across as neurotic. But I love her to pieces x

Does your vet have an emergency number? I'd call them.

Yes I have an emergency number, will ring them now, can't sleep anyway. Thank you xx

I agree, I would call your vet.