breathing difficulty

hello sir here m 23 . from two months im facing breathing problem . two months back i got severe breathing difficulty ,i consulted lungs and heart specialist they told there is no problem  but due  to tension u are feeling like tht , they given tablets i used one month . breathing difficulty is reduced some what . im facing the problem  still now when i m walking then also getting this difficulty some what . some times it is hard to take breathe but this is not severe for me tell me ur suggestion