My chest x-ray showed something wrong but the ct scan was clear. what could it be? they thought it might be a collapsed lung or cancer. i have to wait a week to see the doctor. i am scared.

May be nothing: If the ct was done after the xray, then there is a good chance that there was nothing there. Chest xrays occasionally suggest abnormalities that are not found on ct scans; however, the ct scan is much better at demonstrating pathology. If the ct was normal, i wouldn't worry very much. But, make sure you follow up with your doctor.

CT scans: Are much more sensitive than plain chest x rays. If it was clear, the chest x ray abnormality was probably nothing. It is unlikely that this is cancer.

Shadow, overlap: A chest xray is really a shadow of a patient's lungs and chest, taking 3 dimensions and "squashing" it down into 2. Sometimes, those overlapping structures form a "summation shadow" which can look like a nodule. Since the radiologist wants to be sensitive and not miss a possible problem, they comment about it in the report and perhaps recommend a chest ct.

Relax: Plain chest xray shows sometimes a lot of things but if ct is negative you can relax. I would still quit smoking especially if you are short of breath and apparently you have asthma not quite well controlled on current meds, it will help.