It could possibly be that the April flare ups could be tree pollen, Trees usually pollinate in the spring. The Sept/oct ones could be mold spores that is usually the prime time for those.

One thing that has been known to help with Seasonal itching as well as other things is Dermacton products, comes in a shampoo bar, spray or ointment form and they also do an antibacterial anti fungal ear cleaner and drops.
All natural and the products have often worked where only steroids did before.
If you want to check those out.
Dermacton - Skin Relief for Dogs with Itchy Skin

If you have moved to an area though where there are trees or a lot more trees and certain types and woods, that may be your answer tree pollens in spring
Mold and fungal spores in the late summer/autumn.

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The weird thing is we actually spend the year before in an area which was extremely damp and had loads of leaves. We now only have a few trees.
I will have a look at those products as its always good to try them.

[QUOTE=Jugsmalone;1061543262]Is your house any different from your last place I.e carpets where you are now but wooden floor in old house? This i s just an example. The reason I ask is because my dogs allergy only became apparent when I moved to a house with carpet. He has a dust mite allergy. I was told by a vet also that it was diet related so changed to hypoallgenic but made no difference. Allergy testing is abailable either by blood testing or skin scrapings. I think allergy testing could be the way forward for your dog.

HTH [/QUO The skin allergy test ,though expensive, would maybe be the best option ,but have you thought of spraying your carpets, upholstery etc with Indarex house spray in any case? It kills house dust mites and fleas etc, and most people only need to spray once or twice a year. My dog was tested and found to be allergic to the mite which seemed to be worse in autumn/winter. Atopica tablets (prescription) have relieved most of it and I use the spray also.