Hello Doctor, I Have A 9 Yr Old Grandson That

Hello Doctor, I have a 9 yr old grandson that was tested for allergies. Out of 32 different tests, they found he is highly allergic to cats! He does not have a cat but suffers from year round seasonal allergies! He has a very very stuffy nose almost all the time. I have allergies myself and use Musinex D which seems to help somewhat. Is there any children's medicine out there that we can give Billy? Any suggestions, mainly for a very stuffy nose? Thank you.
Dolores Fazi YYYY@YYYY