Izzy does not have allergies so we are very lucky on that point. She has pancreatitis/SIBO/IBD. She was hospitalized 4 times and almost lost her that many times until we figured out it was SIBO/IBD which triggered the pancreatitis. She was vomiting and throwing up blood and her tummy rumbled like crazy super loud.
We have her on Purina EN but now on better food since she has stabalized. She is also on Tylan/Pepcid/probiotics, etc. etc.
Have you talked to your vet yet?