Brief Answer:
Consult an expert physician.

Detailed Answer:
Hi XXXX,
Thanks for the query under health care magic . I have read it & understand your concern.
Breathlessness with exertion is commonly caused due to pulmonary obstructive diseases( asthma/ bronchitis ) or heart problems. You have already consulted cardiologist & pulmonologist & got investigated to find no abnormality in both the fields.
Few other possibilities I can think of in symptoms like yours are-
- Obesity.. excessive weight gain can cause breathlessness on exertion-due to low levels of circulating oxygen in blood.
You have been advised to reduce your weight & do moderate exercise .. which seems to be difficult because of breathlessness.
In this respect I would suggest to get a check up by an endocrinologist along with few investigations to find probable cause of the weight gain ( diabetes/ thyroid problem ) followed by specific treatment As well diet control as per dietitian's advise .. which would help in weight control & lessen your symptoms.
- Low levels of oxygen in blood can be caused by other two conditions - namely anemia & low blood pressure.
CBC to find Hb% followed by investigations for typing of anemia & it's probable cause would pin point the specific treatment needful.Increase in Hb% in such case gives dramatic result in improvement of symptoms.
Improvement of low blood pressure with life style changes & specific medicines with expert advise helps to control the problem like yours.
* thus consultation of a physician / endocrinologist & as per physician's recommendation ) & necessary investigations to find the root cause of the problem would help you conquering the trouble sum symptom & help you breath smoothly to live a normal & healthy life.
I hope the answer was informative & useful to you. Any follow up query is welcome.
Thank you.

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