B..
N.,
The research and effectiveness of zyrtec with food allergies, is very conflicted. I have many food allergies, and the only thing that helps..is to not eat them. In my experience (I know my personal experience won't be the same as others) the only allergy that gets more severe, is my nut allergy. Each reaction I've had, has been worse then the one before. That is common with anaphylactic allergies.
Have you been to an allergist? You don't specify what kind of Dr. prescribed the Zyrtec. General practitioners are required to know almost nothing about food allergies. It is very rare to find a family Dr. or pediatrician that has a good understanding and education about food allergies. In fact, they often give false, conflicting, and old fashioned advice. I would highly recommended seeing an allergist. They are highly trained and will give you the best results.