Upper back pain shoulder pain. Reason.

I am 27 year old male. I have been working in an IT company for last 2 years . I had been facing upper back pain mostly when lying on my back for more than 2 months. Also pain in arms mostly in right arm but sometime left also. It spread from shoulder to I had consulted the doctor, the doc told me it is because of my bad sitting posture as i work in IT sector. He also asked for vitamin test. My vitamin D came 13.31nmol/lit and vitamin B12 168pg/ml. I am taking the medicine for it. it is 3 month course. It has been 6 days I am taking medicine and my arm is much better but back pain is there. But sometimes I get tinge of blood in my nasal mucus and also muscle kind of pain in upper corner of lung near the neck(on the chest bone) for short duration. I have been smoking for last 1 year around 5 cigarette/day. After searching on net I am in terrible fear as all the symptoms matches with the lung cancer.I am not able to concentrate on my work. is vitamin deficiency the only reason. help