Shortness of Breathing. Causes for this?

Hi,i have been facing difficulties while breathing since last few months,it starts n gets ok on its own but as the prob was consistent since a week with throat pain i went to a general physician,he pescribed Grilinctus-BM,Monticope,Cifran 500 and some Pan 40 and have asked to take them for ten days but after using it for three days,my throat pain is gone but still the breathing trouble is there.This problem has suddenly increased in last 2-3 months...i have had faced a little breathing trouble before aswell but since it got ok in a day or two i ignored it.Moreover i used to smoke before but due to this i have stopped smoking since a month still no improvement.Am i allergic to something?how to find out the causes for this?