Kitten keeps throwing up, and cant keep food down

The first and most serious concern is an intestinal blockage. Is it possible she swallowed a string or some other non-digestible object?

I would at least call the e-vet right now and ask for guidance. I've called my e-vet three times - the front desk asked me questions and in two cases advised me to come in, and one time said stay home and what to look for in case I did need to rush in. It may be she's eating too quickly and just regurgitating, but....

I know the e-vets are expensive, but I'm thinking I'd be calling to take her in, just for my own peace of mind.

Is she keeping water down at all? What happens if you feed her just a tiny bit at a time - can she keep it down?

Possibly. But if she hasn't had any problem before, this is a new thing, and it can quickly lead to dehydration and other problems. I would look in her litter box to see if she's been pooping, and look at her to make sure nothing is protruding from her bottom. If the problem continues, a visit to the e-vet is probably going to be necessary.

Maybe someone else can make some more suggestions.

My second fear would be poisoning, but if she's eating OK, that is very unlikely.

Do you have some hairball medicine? It's usually a lubricant to help it pass through. A hairball can cause an obstruction, but that's not usually the way it happens.

Maybe you could try doing a quick Google search of any vets open on Sunday in your area? I know the Banfield at Petsmart in my area is open on Sundays. It would probably be less expensive than an E-vet. I would definitely try to get the kitten seen soon. Good luck!!!

Most e-vets have to be very upfront about the charges (which are due on the date of service) - many people don't realize that e-vets have, of necessity, higher charges than 'regular' vets and a lot of people will simply be unwilling to pay - or will wait til the pet is in desperate condition and then expect a miracle.

She hasn't pee'd or pooped since yesterday? What happens when you pull up the skin on the back of her neck - does it go back down immediately or stay up. I'd be worried about dehydration. And, like a human baby, kittens can go down very quickly.

Have you tried feeding her a tiny portion of food, or water? Is she not interested at all?

Cats tend to hide pain or distress until it's very late in the game - it can truly be hard for the pet parents to realize something in seriously amiss.

Hairball lubricant is readily available at most grocery stores, Wal-Marts, etc. It might help; it might not. In a severe case, some have given their cats a dab of vaseline. It's not a great solution, but it will work in an emergency. Olive oil or other vegetable oil can work, too, but it depends on getting it down their throats and keeping it down.

How convenient are you to your own vet? Maybe keep an eye on her and get her in to your vet first thing in the morning, if she hasn't improved. You'll have to be your own judge on the matter; if she starts showing signs of dehydration, respiratory distress, serious constipation, etc., those can quickly become emergencies.

One thing you might try is some very liquid soft food. Add some water so that its really soupy. If she readily eats it and keeps it down, then bolting her food might be the problem, although the way this came on suddenly is not promising.

I have a cat that was within a few weeks of turning 1, and started throwing up his food on a Wednesday morning. He was still acting normal so we didn't think too much of it and thought maybe he ate too fast or something random. Friday morning he refused to eat and I tried to force feed a little, which he threw up. The cat stopped acting normal by Friday morning and spent the entire day sleeping alone instead of curling up w/ me or other cats like he normally would.
We called the vet Friday midday and got an appointment and took him Fri afternoon. After they did some testing we found out his kidneys were failing and he had almost no kidney function. The vet recommended that bc of his age it could possibly be some sort of blockage in his kidney versus a kidney failure.

We had to take him to the e-vet Friday when we left the regular vet because the reg vet wasn't set up to do fluids for the weekend and that is what was suggested to us. He spent the weekend on fluids and was fine. The e-vet didn't seem very friendly when we first contacted them but they were very busy which i didn't know until I went there. In the end they were amazing and saved my cat and I appreciate them so much. It is definitely a little more expensive, my e-vet was $100 just to be seen. They saw my cat and detailed a treatment plan, printed it off for us with pricing before doing anything so we knew what to expect.
If you cat starts to become lethargic, especially since it hasn't used the litterbox in a day, I would take the kitty to the vet because things can go downhill quickly! Good luck with everything!