What Causes Shortness Of Breath And Inability To Take Deep Breaths?

Recently I have been suffering from shortness of breath or not being able to catch it. It started about 3 days ago I was able to catch my breath or take deep breaths without stopping short. Now it feels I m on the verge of a panic attack from not being able to breath correctly I can rarely take deep breaths Before I only have the problem on not being able to breath out of one nostril of my nose . It used to switch sides sometimes I couldn t breath out of my left or sometimes out of the right . As far as I ve known i have had the nostril problem but the shortness of breath is starting to worry me. I rarely smoke probably 1 time a month As far as I know I don t remember doing anything wrong to cause this