What Causes Mucous Inside The Lungs With Neck And Shoulder Pain?

I am 32 year old ,5'10 height,80kgs weight .I have some irritation inside my lungs and it wont persist continous .It comes when i sit at too much cold place (ac).and that time mucus develops inside my lungs with normal color ,but no cough.It disappears after few hours or maybe last for one day .It started before 5 months with a slight fever and cough.that time my doctor advices antibiotics ,that time fever and cold went but this irritation was there ,during this irritation occur i have little bit pain on my upper back side near to shoulders and neck .I dont have any pain during breathing and i do excercise daily .