Cat weak 3 days after being spayed

Hi, my cat was spayed about 3-4 days ago. She spent the first three nights at the vet's. When I brought her back on Saturday evening she seemed a bit traumatised and weak, which I thought was normal. She was coming to sleep on my lap and was still eating a little bit.

But today she seems even weaker than yesterday. She's limping and her back left leg trembles when she walks. She won't eat anything at all now and spends the whole day sleeping :'( I'm getting quite worried. Please let me know what I can do to get her to eat.

Thanks