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 tablets. Hope i was helpful. thank you ...take care.