Agree with Karla, just no way to even guess and it would only be guessing. The fact he is eating grass and vomiting probably indicates there is some intestinal issue going on. Have you looked around the house and yard for something he might have gotten into like trash, plants, etc? Hope you can get him to the Vet, if not today, tomorrow. In the mean time, you might want to withhold food or just try some bland chicken (no skin) and rice in small amounts and see if he keeps that down. It is important he has access to water and is drinking.
Please keep us posted.
You need to get him to his Vet immediately before he gets worse.....There are many things that could be going on here & with such limited information, we couldn't begin to guess! Please get him some help ASAP......Karla