Chest Congestion!!

I recently had a massive flu that happened around October end - I have recovered from it but still have fatigue and shortness of breath. The main issue is that if I am exposed to cold air, I get this weird chest congestion that lasts for a day or two which amplifies my fatigue too.

So I visit my doctor and had chest x ray and spirometry - both came as normal.. I am still not convinced - is this some form of bronchitis that takes longer to heal or do I have asthma?

I am also an ex smoker - 5 months free - not sure if it adds to anything!!