I thought my cat was pregnant she got kind of big but yesterday I noticed she was smaller and she is getting sick I would like to know if she had kitten but xant tell how can I tell

She should have some mammary development if she has delivered even one kitten. If she is still in the process, she could still have a, or some, undelivered kittens. In which case, gentle squeezing of her abdomen should reveal their presence. They will, or should feel just like a kitten wrapped in a thin towel... firm, even hard in places like head and legs, and maybe feeling a little larger than it actually is.
If so, she may be trying to miscarry, or have a uterine infection. One good reason to see her vet.

Lacking that, there is one disease that usually produces a 'fat' cat. It's called feline infectious peritonitis, and your vet needs to offer an opinion about that. The fatness is the result of fluid accumulating in the abdomen, but is considerably more involved than just that.

I am presuming she is an outdoor cat, if not both in and out, and not been spayed? Rhetorical question, I realize. But, since we still have no answer, and none likely to be forthcoming, you and she should see her vet, tomorrow would probably be best.

Best wishes.