I am so sorry you are going through this. My Taycie also has a very sensitive GI tract. She struggles with horrible food allergies. And after having test sent to Texas A&M her body produces to much bacteria. In short, she has Small Intestinal Bacteria Overgrowth.
When things are not right, she does throw up, and has horrible diaherra. Like Carmen mentioned my Taycie is also on Tylan powder and she is also on a prescription diet. Once I got the diet figured out she truly has become a different dog.
Tylan powder has also been a lifesaver for us. She has been on it since December and at the beginning of April we decided to slowly wean her of of it. She was off it for 3 weeks and we ended up back at the vet for vomiting. She was given fluids and meds and she is now back on Tylan powder. She truly has no issues while on it. She may and I think will be on this for the rest of her life
I know how scary this is and I hope you are able to find some relief.
Hugs and prayers for you and your little one.