Ooops, your pic didn't come through for me but from what you describe I wondered if you should had a skin scrape done to check for mange?? Haven't heard of it as a reaction to Frontline or Heartguard, maybe others have??? Welcome to the forum, hope to see pics
Ahhh there he is Baxter is a very handsome boy!! You could try some food supplements for the dry skin, salmon oil or sardines. I think I'd still ask the vet about a skin scrape just to be sure. Hopefully Sharon or someone with experience with skin issues will have some other ideas.
I agree it is better to get a scrape done, mange is easier to manage if caught right away. My Kiah had lost hair due to allergies from a food I was feeding her so if it isn't mange it could be allergies. Hope it isn't mange, let us know what the vet says.