Thank you for your query at DoctorSpring.com
I understand your concern.
You have already taken a positive step towards prevention of lung cancer by quitting smoking. So Congratulations for that! There are chances of lung cancer in every smoker, however at the age of 30, you're too young for lung cancer, and that does not seem likely here. If you have given up smoking completely, the effects of smoking will be reversed very soon, and you won't have to worry at all.
But you do seem to have chronic pharyngitis, hence the streak of blood. Especially with the classical post nasal drip that you have, it keeps irritating the pharyngeal mucosa, providing a continuous nidus for infection, can even manifest subclinically. However, post nasal drip ( mucus dropping from back of nose to throat ), is one of the commonest causes of chronic pharyngitis.
You need to get yourself examined by an ENT surgeon for the same, who can also guide you about the tonsillar stones. The throat secretions need to be cultured, and based on that appropriate antibiotics can be initiated.
Hope this was helpful,