need help new to site asap.

Okay idk where I should post this but I have a 9 month old kitten. And I recently changed his food and we bought it yesterday fed him and since then he's been throwing up food and now its brown liquid I have no idea what to do. And he has been to the vet nothings wrong only animal in the home. Its like everytime he gets up he throws up. I havnt fed him yet becuz I'm scared. I don't want him to die I am a first time animal care taker he is a rescue. I've had him since he was able to leave his mom. And he's been on this food before idk what's going on.

The first thing to do to is go back to the old food, whatever it was you were feeding him BEFORE he starting throwing up.  If he doesn't throw up on that then he's fine, and stick with that food at least for now. If he continues to throw up see a vet immediately.

You cannot stop feeding him because you are afraid he will throw up. Return to the old food immediately.

What were you feeding him originally and what is the food that he is throwing up on?

Agreed that a return to the old food is necessary.  Anytime I've changed food for my cats I've done so very slowly and it's been done over a period of weeks.  The change can be very hard for their little tummies to tolerate.  Have you been to the vet since the vomiting began?  If the food is not the culprit perhaps it's time for a second opinion with a different vet. 

If it's dry food, you'll need to gradually introduce it over the next couple of weeks.  So, return to old food, then once he's stabilized, add a bit of the new food to the mix.  Keep this up for a few days, then add a bit more to the mix for a few days and continue until you've got just the new food.  If you're feeding canned food, you don't have to do the gradual introduction of new food as it's not so hard on the system.