Is there something wrong with Otis?

My cat was gone for three weeks, and came back pretty skinny, so I ume she didn't eat anything the entire time she was gone. When she came back I knew not to give her too much food, or else she'd get sick, not being able to eat while she was gone. For the first four days she was home she didn't throw up or anything, she was fine, but then she started throwing up. It seems to be getting better, considering she used to puke right after eating and now it's hours after. I give her liquids, not hard food, and make her food mushy with water. She still pukes, but not as much. I was just wondering what could be wrong with her? About the vet, i won't have money enough to take her until after the first of the month, so I need helpful advice please, if you can give it. Thanks !