Have you considered using a neti pot and cleaning out your nasal passages that way.
It's a saline (water & salt) solution to clean you out naturally.
I suggested this to a friend who was taking several allergy pills a day, now she's down to one every week or so.
No guarantees, but a simple and natural suggestion that worked for me and others.
Nasal irrigation - Wikipedia, the free encyclopedia I use the blue and clear type.
Do Neti Pots Really Work? Doctors recommend nasal irrigation, too.
I would be cautious about "blockers" - in many cases an allergy is a block.
For example, if you're allergic to Vitamin C, your body can be blocking the absorption of Vitamin C - throwing too much Vitamin C at your body may result in other systems going a bit haywire.