Shortness of breath is the result of weakness
While weakness may have many indirect causes - the common cause always is lack of efforts to grow and to be strong. Instead of focusing on breathing - focus on working harder and growing your body strong and healthy, then all symptoms of weakness will vanish in the achieved inner and outer strength.
Shortness of breath is the result of weakness - inside and outside - grow strong and your lungs are stronger and larger as well.
Body adapts to its usefulness or uselessness. Body can be used or abused. NON-use is equal to abuse and hence body starts to deteriorate and growing weak. God gave body to use body. God created thousands of muscles to use thousands of muscles to help others, to protect others, to feed others, to heal others, to shelter others, ...
Strength as a result of solid work will result in stronger lungs and hence deeper breath and longer breath-holding times where needed such as US sports, water sports, etc. All the outdoor activities I recommended are ideal to overcome exactly those symptoms.
Years of outdoor PT, outdoor recreation and finally outdoor work will cure your illness. It takes years of persistent change in life style thousands of hours of real training, work and practice - the older you get the harder it APPEARS - the more you may have to kick your own butt to overcome the practiced weakness of the past. However: anything always is possible. It's just a matter of willpower and that is a matter of clear decision to BE strong.
Your work of the past many years never offered any challenge to grow strong or for the body to be of any use at all - hence the body simply adapted to your way of using non-using it.
I have given you all you need to overcome that - already many years ago - now it's time to enjoy the workout, outdoor work and outdoor activities - more and more each day - in any weather, any climate, any temperature, any mood - just keep on doing each day and you shall succeed if you want so.
God bless
hans