Dude, now I know why you were always so edgy in the past...too jacked up on antihistamins! Those things can really jack you up pretty bad. They used to put give me those @#$# cortizone injections when I was in school. That was rough.
Probably, your metabolism is starting to slope off, so the drugs affect you more now. I used to never be affected by Benadryl either, until I hit about 20 and they started knocking me out so I switched to plain old Psuedophed to open up my head each morning--but that can jack up your blood pressure if you take too much. It's a tough call. I've found some Bromphen/Psuedophed combos work pretty good. I don't know a name brand for OTC, but you can check the label ingredients--it might be a generic version in the Dimetapp line I've been taking. It works well for my daughter too. They put her on a prescription strength version with cough suppressant once--think it was called Bromphemex or something like that. (damn generic labels).
For maintenance, they put my daughter on Zirtec nightly. It seems to do the trick. If she's having a really hard time with it, I'll switch her to Claritin in the mornings and give her Benadryl at night.
It's always a good idea to switch up your meds periodically, or try to go without for a few days to sort of flush the system. Eventually you build up a tolerance for any drug if you take it long enough--especially with antihistamines.
Good Luck dude!
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.