Make SURE you get tested for as many allergies as possible. Make sure your doctor knows that you suspect food AND environmental allergies due to your many respiratory symptoms.
Faith mentions a lot of useful information but you need to address your intestines more then anything. Yeast, Parasites, and h. pylori are causing your intestinal inflammation, malabsorption, intestinal permeability, etc.
That's the root cause, MCS is a symptom.
You should start looking into diet and natural anti-microbials such as
Oil of oregano, Grapefruit Seed extract, coconut oil, Garlic, etc.
Also if safe, try the Rx route if the naturals are not enough. ABX are an absolute last option and should be avoided. Period.
Once you get your allergy results you can adjust your lifestyle as needed and start treating the results of your CDSA.