Your symptoms suggest that your airways may be becoming sensitive to cold air. In many people, this may be related to asthma or an allergy triggered by temperature change. A history of wheezing also supports the possibility of asthma or a similar airway condition. Cold air can tighten the airways and cause excess mucus production, leading to cough and breathlessness. Hypothyroidism (underactive thyroid) is usually not the direct cause of these breathing symptoms. If you are taking thyroxine regularly, it is important to continue it and also check your thyroid levels as advised by your doctor. You should consult a doctor for a proper evaluation and treatment. The doctor may suggest a breathing test to assess lung function and determine whether you need an inhaler to prevent or relieve symptoms. In the meantime, avoid sudden exposure to cold air, cover your nose and mouth with a cloth in cold weather, and try to breathe through a scarf. Avoid smoke, dust and strong smells, as these can worsen symptoms. Regular follow-up is important to keep both your breathing and thyroid condition under control.