How can I minimize allergy to pollen from trees & grass?

Hello,

I need help. Every spring (May, June) I have severe allergy to pollen from all trees & grass. Since I training and play games a lot outdoor (baseball) and all around there are trees and grass I have questions for all of you that might somehow help me.
How can I minimize allergy?
I tried many drugs like Claritine and other drugs for allergy, tried injections etc. to lower problems but it seems that nothing helps me.
Does somebody have some succesful solution to this problem?
Please help.