Oh my...you poor thing and poor little sirius....you have been through so much.
Coccidia is not worms, they are microscopic parasites that live in the intestine and is usually treated with albon which is a sulfa based med. Read this thread for a lot of info. Post #21 I think of that thread describes what it is exactly.
http://www.yorkietalk.com/forums/sho...light=coccidia
When Buddha got a tummy ache from being fed ham at 11 weeks, he refused to eat and got hypoglycemic and developed coccidiosis from the stress. The breeder knew he was allergic to albon because she had given it as a preventative and he had become sick so she told me to tell the vet he was allergic. WELL< the vet was still going to give him Albon and i said no way....the vet "wrote him off" and basically said he was going to die, but my breeder treated him with chorid instead which is not sulfa based and we syringe fed him around the clock for two weeks and he is healthy and happy and thriving today!
Unfortunately vets don't know everything and sometimes we have to do our own research and even take the advice of well seasoned and experienced breeders who know from experience what is best for this breed. I have never heard of Drontal but if Kimberley found on the interent the info about vomiting and your vet didn't know about it, that is concerning.
If he is not eating and you need to syringe feed him make a mixture of bay rice cereal, pedialyte and cornstarch or karo syrup until it is the consistency of runny oatmeal and feed him about two 15 cc syringe size feedings every three hours or so. Give him pedialyte by syringe as well to keep him hydrated. Sometimes they will eat the puppy colostrum you can get at the pet food store too.
Good luck.