I Have A Type Of Lung Condition That Only Responds

I have a type of lung condition that only responds to Singular. I recently took an allergy test where I was tested for 81 common allergens. I did not get any raised welts on my skin, but I had itching in my bronchial area and lungs. My breathing became difficult. The doctor treated me with albuterol and benedryl. He then wrote a prescription for singular which works dramatically. Why does the singular work and what is the difference between it and regular antihistamines?