Breathing Issues. Weight? or any other?

I have been facing an issue with my breathing of late. Previously I used to breath heavily whenever I walk for half a kilometre or took stairs for just one floor during winters only. Breathing will be so heavy that i will be suffocating for air for few minutes. But now this is happening on hot days also. Even my normal walking speeds also causes this to happen. Is this issue related to my weight? Or any other? I need advice in this. My height 5'4" and my weight is 70kgs. I neglected this issue till now thinking that I am less active. I started to walk for 3/4 kilometres daily in hope that this issue goes off. But still whenever I make a short visit or take stairs, this breathing issue recurs. Kindly advice me how to overcome this issue. Thanks.