13 week old infant has allergies

Where it has been commonly believed that children under three can't develop allergies to  airborne allergens our son has. He has had nose congestion since he was six weeks old. He has been pricked and injection tested and so far shows allergic to mold,dust mites, cockroaches, & pet dander.  My question is if anyone has had any experience in treating the symptoms at this age? We have taken the steps in our home to remove/trap as many of the allergens as possible. We have also tried four diffrent types of childrens perscription treatments, which have all caused negative side effects even at the very low dosage schedule.
If any one has any experience for treatment at this level we'd appreciate input.
Thanks