Hi H.,
I responded earlier to your other question. I am still unclear as to what the allergy medication is for. Is he having an allergic reaction of some sort? Allergies are more sneezing, watery eyes, itchy eyes, itchy nose, itchiness overall and hives kind of thing.
So if he hasn't responded to the Claritin then I am thinking maybe he's not having an allergic reaction.
You don't mention how long you've waited before writing this. We find it takes about an hour or two with our kids and my husband when he takes allergy pills. Some work faster than others. And some take days to build up in your system - so that you take them continuously.
Again, if you're not seeing the results you expected or have questions about this - I'd ask your allergist.
Good luck hope he's feeling better soon