I cant breath , i have shortness of breath and im getting paranoid

[MaragkakisP]

Hello to all,
i have been suffering for shortness of breath as i feel it i cant breath normally and sometimes suffocating, i am a smoker for more than 15 years and im 31 years old.
I try to take deep breaths and it seems that the air is not enough , i have this problem for some years now but it came and gone as it pleased.
1 month now it became worse after a flu that i passed that required antibiotics to pass and its becoming worse and worse every day. The symptoms are as followed : one cough in morning with a big flem of black residue and during the day its becoming worse but with no apparent residue like the morning , feeling out of breath need to take more air and last if i choke on food or water it needs about 2 3 minutes to recover and my breath stops for 10 to 15 seconds, Half of the times it feels like someone is sitting on my chest and im gasping for a breth and sometimes it feels like half of my lung is not functioning.
Doctor tests X ray, spirometer , cardiac diagram , blood test ,allergy test and throat doctor couldnt find anything with the little camera through the nose except little problem in throat but he blamed it on acid reflux but i know i dont have it cause i dont feel burn like when you throw up and after.   Everything showed normal for a smoker.
I have been between doctors and they cant find anything in particular for my condition.
Im getting paranoid and i dont know how to get rid of that cause it stops me from doing my daily normal activities even going to work is a nightmare cause i work in a kitchen for 2 years now and its pilling up.
If someone can help me or direct me i would be most gratefull.
Maybe im not describing it so good so if someone can ask me specific questions for symptom evaluation that would be great.
Thank you in advance.!