Take it to vet as soon as possible as it seems to be stomach problem. In most pets there are abscessed teeth. So do not worry about it. Change its food and see the results. Don’t let it eat bad things from outside.

 Ooh, I hope you have taken him / her to the vet by now, or that she is better. I hope your kitty is eating and all better. This site says that your question still needs answering, so I hope that you have neglected to note that your question is done and answered, rather than neglecting the cat.