I have a 2.5 pounder that has vomited all of her life for no reason. (She is 6 yrs now) Many vets and tests and no medical reason for it. She even stops eating and I have to feed her baby food. The vets say that she has a nervous stomach.
The main thing to the vomiting is to not let them get dehydrated. I keep Pedialyte here all of the time. I hope this helps.
I’ll keep your baby in my prayer.