Hi welcome to Healthcare Magic....
Breathlessness on exertion and easy fatiguebility can be due to several reasons .
Most common cause in a female being ANAEMIA
i.e low heamoglobin.
Most common cause for Low heamoglobin is iron deficiency
In females because of monthly periods , they loose blood and hence are more prone to anaemia than men.
However heart or lung problems can also cause your symptoms.
So my advice would be visit a physician( to check your heart and lung status) , get few blood tests done - 1) CBC-complete blood counts 2) Iron profile 3) Peripheral smear , these 3 basic blood tests tell you , the reason for low heamoglobin and you can be treated accordingly with ferrous sulphate
tabs and Vit B12 and folic acid
Hope i was helpful.
thank you ...take care.