A doctor would be able to do a blood test to see if you were anaemic and required a supplement of
iron. Folic acid helps with the absorption of
iron.
Foods rich in iron are liver, kidneys, dark greens, cereals are fortified with iron. You may find more.
Like you mentioned asthma - you would have a persistent cough too with that and gasping for air. The doctor can do a simple lung function test at his surgery to find out whether you have become asthmatic or not.