I am an ex smoker.4 weeks now. but when i go for a walk, any uphill makes my inhaling difficult. my spirometry shows everything is okay.

Still a problem: You may have exercise-induced asthma. The spirometry is being done when you are not exercising, though that is when you are having symptoms. It is also possible you are deconditioned. You may benefit from using an albuterol inhaler before exercise or exertion. Major congratulations, btw, on quitting smoking. You will never regret it.

See doctor: You may have exercise-induced asthma (vs exercise induced bronchospasm which occurs mainly with very strenuous exercise). Consult your doctor since cardiac disease and other lung conditions can cause breathing problem as well. A pre-exercise bronchodilator may be tried.

Hard to say: people who are not used to exercise get short-of-breath sometimes with very mild or moderate exercise, and you can have that just from being "deconditioned" without any underlying lung disease. However, heart problems can also cause shortness of breath, especially with exertion. Congrats on stopping smoking, but have a conversation with your doctor about your exercise intolerance.