Please quit at all costs. I am 43 and smoked for 26 years...I now have Emphysema! I kept telling myself , "I'm young, I have plenty of time left", and now I realize I was lieing to myself. There is a wonderful smoking sessation product out now called Chantix...ask your doctor about it! I had tried everything to quit..the patch (twice), gums, candies, Welbutrin (twice), cold turkey etc...Nothing helped...but the Chantix helpeed me quit. It blocks the pleasure receptors in the brain that tell you you want another cigarette. As for the blood, it could be a number of things, I would see a Doctor to be safe. It could be just sinus damage, or lung damage, throat or even a sign of an ulcer. To be safe, and for your piece of mind, I'd say to see your Dr. and ask about the Chantix while you are there.
The smoking is causing changes in your lung that cause inflammation. It is not uncommon to have small amounts of blood when this inflammation is further irritated by coughing. The damage caused by smoking occurs whenever you smoke. People 'feel fine' until the changes have created a significant problem. Emphysema and chronic bronchitis get a diagnosis on a specific day, but have been going on for years before that day occurs!
If the blood is continuing, even in small amounts, you should call your physician. A chest x-ray may be needed.
Trying to stop implies you are ready to make this important change in your life. It is not easy to do and many people fail several times before succeeding. There are many programs, most of them free, that can help you to do this.