Cat vomiting blood

Hey guys. So Tuesday night my tub was full of blood my cats sleeps there every night. Today at night he threw up again. What can i do? I changed his food like 4 days ago. Could it be the food? At times when im not home i leave him locked up in the restroom can it also be his litter box?

Give your vet a call, it doesn't cost any money to enquire if they think you should take her in.