I am very allergic to grass pollen - this last week has been just horrendous. The only way I am managing my symptoms (mostly itchy and swollen eyes) is by using a fexofenadine first thing when I get up, and then taking a piriton during the day when I feel I need to. And using eye drops.
I feel OK, not overly drowsy. Sure I read somewhere that exceeding the recommended dose of antihistamines wasn't so awful.