Hi groz, the shortness of breath often caused by chronic bronchitis, allergy, anemia, some diseases or infections of the respiratory system and heart diseases. Also people with lung cancer will constantly experience this symptom[SUP].[/SUP]Most periods of breathlessness are not severe. However, you will need to consult the doctor in case shortness of breath happens with no obvious trigger, while you are resting, causing trouble to your sleep at night as well as having such symptoms as chest pain, fever, wheezing and tightness at chest or throat.
Over all, it happens when your heart is unable to pump enough blood to supply oxygen to your body
I have searched some methods for the shortness of breath and here what I found, I hope they can help you improve respire system

- Steam inhalation: against breathlessness caused by some respiratory problems as it is capable of decongesting the nasal passages.
Furthermore, moisture and heat from steam will break down and dilute mucus in order to eliminate easier.
Take a bowl and fill it with extremely hot water, put in some essential oil like peppermint or eucalyptus oil. Put your face above the bowl with a towel over the head. Breathe in the steam deeply for 15 minutes. You can apply this method whenever you are suffering from nasal congestion.
- Deep Breathing: Lie yourself down on the back, take your hands and put on abdomen while relaxing the muscles. Breathe deeply by the nose, enlarge the abdomen and inflate the lungs with air. Keep the breath for few seconds. Exhale slowly by the mouth and deflate completely the lungs. Perform for 5 – 10 minutes in 2 to 3 times per day.
This method is also great for COPD (chronic obstructive pulmonary disease) patients.
They have many more methods but I just believe those 2 the most.
At the end, I think you should tell your situation to your doctor.