Cat Vomiting

Hi guys, I need a bit of urgent help. My 10 year old (mostly) indoor cat has been vomiting everything she eats for the past two months off and on. I took her to the vet, everything came back negative both stool sample and blood work. No thyroid issues or kidney problems. She’s loosing a lot of weight, I’ve switched her diet multiple times to see if she can handle it. Purina one sensitive stomach, hills perfect
Digestion and nothing someone please help.