Why do I have a weak immune system?

I have severe allergies, seasonal and chronic, I get sick often and recover slowly. Hay fever can leave me bedridden for days and many medications don't work for me. But I don't understand why. I eat healthy, whole organic foods, never eat processed foods, and exercise daily. I don't smoke cigarettes, I maintain proper hygiene....I mean, I shower daily and even floss every night. I go to the dentist and doctor when in supposed to. I live in a rural area, get plenty of fresh air and am not exposed to environmental toxins. I use hypoallergenic bedding and cleaners, all my clothes are made of natural fibers. But this all doesn't stop me from getting frequent viruses and colds that last a long time, or from sneezing and itching during allergy season. I'm starting immunotherapy soon but I'm dubious as to how effective it will be. No amount of medication in the past has seemed to ease symptoms, or work like it does for others. Im sure it's not a karma issue either, lol...I pay my taxes on time and volunteer. I get so angry when my best friend boasts how he can eat whatever he wants, keep a messy house and never visit a doctor, and still be a picture of health. Was I just born this way? What else can I do to boost my immune system? I dont take vitamins, is that it? I'm desperate to live my life without being sick all the time.