i'm not a nurse or pharmacist, but my understanding is..
Zyrtec/Claritin are both Cetirizine and Loratadine, are all in the most recent class of -drine, and they work similarly to target hay fever/seasonal allergies. Allegra, as well. My understanding is they all work nearly the same, but work more efficiently for some than others due to a variety of cir***stances/allergies.
Benadryl is Diphen, which is slightly different and an older generation, and better targeted at skin allergies like hives, rashes, and contact allergies (i.e.: latex allergy, contact only peanut allergy), rather than seasonal allergies due to pollen/dust, etc. it also has drowsiness and increased appetite/hunger as major side effects. So much on the drowsiness bit, that the only difference between Tylenol and Tylenol PM is that Tylenol PM has Diphen added to it.
and that this year is the "worst year on record" for allergies.
so say... scientists or whatever Spring 2012 Could Be Worst Ever for Allergies - ABC News
i hope yours get better soon though.
you're to pretty for allergies, R!