Westie stomach issues Questions

Hi i have a 14 year old westie girl. She has always been in excellent health. About 4 months ago she started throwing up. It's usually always a very pungent bile. She does have allergies. She's on allergy drops that her dermatologist makes up for her according to her allergies. She was on royal canin potato and rabbit for her allergies. Vet recently changed her to Royal Canin Hydrolyzed diet to see if that was the problem. The vet also did a sonogram to make sure there weren't any blockages or cancer. Blood came back great for all major organs. I have changed her to eating 4 meals a day to keep food in her belly at all times. It has helped some but she still throws up. My previous westie did the same thing but i wasn't as tuned in to her health as i am with this one. Vet also tried many meds that seemed to make her worse. I have stopped all meds except her allergy drops. Any one have similar problems and found a solution. Thank you in advance