Steve, my husband gets the same effects as you do from Piriton - it turns him into a dozy zombie. My (doctor) sister has recommended many alternatives, but they all seem to make him very sleepy.
When in Africa, I too have been eaten alive by mozzies, and I can't stand bloomin' Deet either! At least I take the usual anti-malarials (Malarone tablets) and have never had malaria.
Husband can't seem to sneeze quietly ("AAAAAAACHOOOOOOOOO!") and his poor nose, (which is flat and small with very open nostrils, like all Africans) just lets in the pollen very easily. He had no contact with tree/grass pollen before he came to the UK, so it's hit him hard.