hi, sorry I can't comment on the herb or the Triamcinolone but like all steroids there are many side effects....do speak with your Vet and tell them whats happening.
Atopica(cyclosporine) is prescribed OFF label for cats...usually to treat Feline Granuloma Comlpex. the side effects are less than that of steroids.esp for long term use. .
http://www.marvistavet.com/html/body_cyclosporine.html
I am very sorry to read your dear kitty has this disease, it sounds like it going to be a tough road to control the symptoms and give him some relief...the write up I did find for information is for dogs, but obviously cats can also have.I will include it and hope it helps,
the very best of luck to you and your dear kitty, please post again if we can offer any help...♥
http://www.marvistavet.com/html/body_pemphigus_foliaceus.html
Pemphigus foliaceus is an autoimmune disease typically treated with steroids to get it under control and then a less strident topical or oral medication to keep the development of new blisters in check and prevent existing ones from becoming infected. Atopica is intended for in dogs with atopic dermatitis, so I don't know how this would be helpful to your cat and could be harmful since I don't think there have been any studies does regarding it's safety for cats. Triamcinolone is a steroid which does have side effects, vomiting being a very common one. San Ren Tang is an herb with only anecdotal info on it's effectiveness. It is generally used for digestive issues (constipation, diarrhea, bloating, etc.
Have you gotten back to your vet to tell him about the vomiting? He may be able to prescribe a different steroid or change the dosage to alleviate the vomiting or prescribe an additional medication/diet to alleviate the vomiting.
Relatively speaking, pemphigus foliaceus is the more serious issue and can be fatal if not treated quickly and aggressively. I would not recommend stopping or reducing the dosage unless specifically directed by a vet. You and your cat may just need to put up with the vomiting temporarily until the immune disease is well controlled.