Pulmonary fibrosis causing shortness of breath, dizziness ?

Dear all,

I am 23 years old male, having almost 4 months:
- shortness of breath(always/anytime), can not take deep breath.
- palpitation(sometimes)
- tingling sensation on my upper back, my finger and my foot (very often)
- dizzy, feeling weak.

I had a history on asthma, but my SOB didn't response to asthma medication. Recently, my doctor prescribed me Singulair, Allegra, Xopenex, Flovent (since he told me that my SOB is because of asthma). I did 3 chest x-ray tests (last one was 2 weeks ago, came out normal), spirometry test, EKG, Echo, holter monitoring, TSH blood test. All test were normal. With this SOB I can't concentrate while studying and doing another activities. My peak flow is around 500 L/min while the normal for my age and height is around 610. (I'm 5'7" high)

My questions are:
1. Is it possible that my SOB is because of Pulmonary Fibrosis/Interstitial Lung Disease? I was a motorbike rider when I was an undergraduate student. Is the exposure of air pollution (from vehicle for example) can cause Pulm. Fibrosis?

2. What kind of test need to be done to know whether my SOB is because of Pulmonary Fibrosis or not?

3. Does normal chest x-ray result can rule out Pulmonary Fibrosis/Interstitial Lung Disease?Do I need to have CT scan on my Lung?

Thank you very much

Heribertus