How To Treat Shortness Of Breath And Chest Pain While Playing?

Hi, my name is Mark, 23 Years of age. I am just bothered about the whistling sound I hear whenever I exhale. It is like a whistling sound u hear when you breathe through your nose. I had asthma when I was a kid. But then It disappeared when I went to secondary school and college. I often play basketball and doenst suffer from any short breaths or chest pains. I smoked for 4 years and stopped 2 weeks ago. Every morning I feel like theres phlem in my throught or lungs but really unsure of what causes the whistle sound? I ve been hearing the whistle sound for 6 days now.