Do X-rays Diagnose Asthma or Are They for Routine Checks?

Question

When I went to the allergist last time, he told me that my asthma has become so severe that he cannot treat me any more for it. He informed that my Pulmonary Function Test readings were steadily dropping every month and that he did not know what to do next. He asked me to take an X-ray of my chest and referred me to a Pulmonologist. The fact is that I am not insured so it is quite expensive to have an X-ray taken and to see a new Pulmonologist together. So I was wondering whether the X-ray is just to confirm that I have asthma or whether it is just a routine check when symptoms begin to get very severe.