My cat keeps being sick?

If your cat is trying to bring up a hairball a little liquid paraffin will help. (It isn't the stuff you burn) It is available at pet shops. DO NOT give loads or over more than 3 days as it stops the cat from absorbing certain vitamins and therefore can cause long term damage if constantly used. It has helped my cats in the past. It softens and lubricates the ball making it easier to bring up or p through. If he is bringing up all his food and is losing weight get him to a vet as he may have swallowed something that has caused a blockage. My youngest had to have a piece of intestine removed when he was about 9 months old as he chewed off the finger end of a washing up glove and it got stuck preventing food from ping through. He is 12 now and very healthy, thanks to an excellent vet. I hope this helps.