Zyrtec seemed to do very little for us, so was not worth the effort. Singular was a little better. Allegra helps my son best and when he stays on it at his worst time of year, he does not get sick like the rest of us! LOL
Claratin and others with the same base ingredient 'Loratadine'
do help but they seem to dull our processes. We are not sleepy or sluggish, but cannot think. We suddenly cannot do simple things like 2x11=22. We only take it when our allergies are absolutely getting the best of us.
The thing that my son took at your son's age was Rynatan. It was in a liquid form and he took day and night. It is a type of decongestant. It worked wonderfully for him and the only reason we quit taking it was convenience sake. When he got old enough to spend the night at friends houses, it was difficult to see that he got it. So we switched to pills and that is about the time all of these different allergy meds became so available and widely used. We went through several looking for one that would help him.
Good luck