Only right after smoking i get horrible upper back pain than it goes away after awhile until the next cigg. i'm quitting. but why is this happening. s?

Not sure of this: unusual symptom, but when you are dragging on a cigarette I would imagine you would have to use your lung/ mediastinal muscles. A blood clot in the lungs could cause pain when you take deep breaths. GO see your doctor. Or muscle injury (intercostal muscle between the ribs). But congratulations on quitting smoking since you have taken the biggest step to have a healthier life ahead of you.