Chronic chest pain. For around 4 months.

I have chronic chest pain for around 4 months. I don't feel any pain in normal body posture but when I tightens my chest, I feel a kind of pain in my upper chest portion. Further, I am not able to find a specific location of pain, as someday, the pain is in upper part of left chest or someday the pain is in upper part of right chest. The pain is also followed by mucus production in morning and I always feel as if something is getting stuck in my throat. I don't have any difficulty in breathing and swallowing food. But generally, after having food, I feel a kind of sensation to cough and a bit difficulty in breathing. I have history of smoking for 4 years. I have quit it for around 4 months.