At least when I had poison ivy last year it seemed to help more. My allergist gave me some sample tubes of some stuff to treat blisters on my arm, but even the over the counter 1% stuff may help. Calamine just turned my arm pink and left flakes everywhere as it dried and fell off, though [link|http://www.aad.org/pamphlets/PoisonIvy.html|this] dermatology page says OTC hydrocortisone doesn't help as it's not strong enough. YMMV.
I've heard from several people that eating poison ivy when you're young gives you immunity, but never tried it myself.
Itching is a nasty thing... Of all my childhood illnesses, I hated chicken pox the worst. :-(
Best of luck.
Cheers,
Scott.