Nessisary exposure to allergens

This year I plan to put in a significant number of hours helping with many duties associated with things I am allergic to. Claritin D seems to do the trick but I am wondering if there is a way to increase the resistance to these allergens simply because the symptoms are not by any means deadly but make it difficult to do my job.

Claritin D contains 10mg of Loratadine to act as its antihistamine. I am guessing this is the maximum that should be taken at any time?

Pretty much anything the blows in the wind applies to me as well with the exception of sawdust and for whatever reason sunflower dust (unable to determine why).