Bravecto?
Another good FB group is Natural Care for Animals and People. Dorwest Herbs in the UK will also give out helpful advice.
Personally I would only consult with a homeopathic vet now for a problem like this. They have had extra training as a Homeopath, as well as being I fully trained vet. You can also call Ainsworths Homeopaths in London for excellent free advice. The British Association of Homeopathic Vets have a countrywide list, but many of them will do phone consults. What part of the country are you in?