What could make my 8 yr old spayed female cat bloated overnight?

She continued to vomit sometimes twice a day. Sometimes she would vomit her food and sometimes it was clear. I tried hairball treatment but that didn't seem to help so I took her to the vet to get her checked out. She's tested negative for parasites, leukemia/feline aids, and her organs seem to be working fine. Although, her red and white blood cell count is low too. Any ideas?

put a touch of soft butter on her nose. she will clean it and by swallowing the butter it will help her, if anything is obstructing her airway or such.
chicken broth is great. warm it up,if she will not drink it, use a little eyedropper and a few times an hour give her some. Also get some vitamin water and do the same.
Place her over your knees and gently pat her back in a motion towards her head. this may dislodge something.
A 1/4 teaspoon of pink pepto will help very much.
I hope this helps. let me know.

Ok..BAD news here...i'm sure your vet did not do something called an fip titer test. Your cat does have all the symptoms..bloating is the abdomen is caused by fluid in fip. EVEN though your cat has the symptoms..(mine did also)..it doesn't mean your cat has it..mind did not and i was pretty sure at the time. Fip is rare and usually found in shelter cats..the cat almost always runs a slight fever.
You can do one of two things..you can do the titer test which will give you a pretty good idea if the cat has it..or you can have your vet draw some fluid out of the abdomen and send it to a lab...most vets know right away by the color of the fluid if they are familiar with fip.
There is no cure for it i'm sorry to say....please have your vet do the test.
When you say bloating is her abdomen very swollen?...I am sorry to say again this looks like a typical fip case.
Please let me know how you make out.
I'm sorry.

im stumped, might need more tests, i don't know. im sorry, wish i could be more help! hope your kitty gets well soon!!

The vet is the one to ask.