I’m A 63 Yr Old Female. When I Eat, I

I’m a 63 yr old female. When I eat, I have to consume much smaller portions than usual, otherwise I vomit. I’ve lost about 17 lbs in 10 weeks. I do need to Lose weight, but now am becoming concerned as to why this is happening. I don’t feel nauseated, but am very aware of the need to throw up unless I eat a very small portion.