you need to be clear about exact kind of breathing problem you are having. one is nose block where you will have mouth breathing and related problems such as dryness of mouth, frequent throat infections etc. other one is difficulty in doing normal breathing with normal functioning of nose which is mainly due to problems related to your lower respiratory tract such as windpipe and lungs.
if you have nose block then causes can be many from sinus problems to polyps in the nose
if you have difficulty in breathing normally with normal nose you need to consult chest physician or pulmanologist for complete evaluation of lower airway