Cat not eating

My cat had kittens 9 weeks ago but now she is left with a uterus infection which she is still on antibotics for as soon as she is better she can have her spay but the problem is my cat won't eat iv tried everything and the vet said she really need to put on some weight but didn't give any suggestions to how I can get her to eat iv tried all tin foods for her also chicken and fish but its always left in her bowl

You could try meat baby food (without onions and garlic). A lot of our members have had luck with that. Adding the juice from water-packed tuna to her tinned food, or sprinkling a little bit of Parmesan cheese on top might entice her. Have you tried warming up her food a little by zapping it in the microwave for a few seconds and stirring it to avoid hot spots? The vet should be able to give you an appetite stimulant, too.

How long has it been since she ate? Are the kittens still nursing?

A few months ago I also went through a saga with my cat who would not eat (http://www.thecatsite.com/t/259470/vomiting-bile-possible-blockage-in-ragodoll-what-to-ask-vet). What worked for me was a combo of cerenia and cyproheptadine-these two are wonder drugs in my opinion. If your cat has not eaten for a couple of days you need to get nutrition in her right away to stave off fatty liver and as she is nursing it is very important she gets enough calories. I know a lot of people are scared and for some reason a lot of vets also don't recommend but syringe feeding is a life saver. Carolina has a great thread on how to syringe feed and I promise it is not as bad as you think (http://www.thecatsite.com/t/227858/syringe-feeding-lucky-video-if-your-cat-is-not-eating).