What Causes Tightness In The Chest Causing Difficulty To Breathe?

When I get sick, it is typically a lung related illness, which ends up lasting over a month. Even when I am well, I can feel a sort of scraping or rattling in my chest in a very specific spot upon deep inhalation. I have had X-rays to see if anything could be seen and there was nothing. My doctor has not been able to hear what I am talking about either. I also become unable to breathe with vigorous cardio exercise. It is not normal breathlessness. My chest becomes so tight I cannot inhale. I have tried inhalers but haven t seen great results. Also, when I am sick, I often have black streaks in my nasal discharge upon blowing my nose. I do not smoke (never have), I do not have exposure to dirt/dust/pollution. The black streaks only occur when I am sick with one of these respiratory illnesses. Please let me know what your opinion is.