If you have carpets I would recommend shampooing them all, spraying them with the febreeze allergen after and then vacuuming really well before and after. We had a similar situation, and this helped our little girl so much! We couldn't afford at the time to rip all of the carpets out! However, we did eventually and it did help, but you have to sweep daily! Also vacuum your vents and and returns... Our son also had a similar situation, and he had his tonsils and adnoids removed. It made a world of difference for his immune system! He NEVER gets sick, although he still has asthma. He has been diagnosed with a corn allergy and we have to avoid ALL corn and corn derived foods: corn starch, high fructose corn syrup, maltodextrin, dextrose, etc. Just a thought. It has improved his quality of life, happiness, eczema, asthma, etc. He has also been diagnosed with allergies to pumpkin and outdoor molds.
Good luck. We didn't get our sons issues "fixed" until he was 3! And it took lots of effort (and still does).