Blood in spit severs on smoking, stopped smoking, feeling of dripping at the back of nose to throat, difficulty in swallowing. Cause?

I m a 21 year old male, i smoke (average), about a week ago i noticed very light blood when i spit and it seemed to get worse when i smoke. i stopped smoking immediately after i noticed that and its been about 5 days, the blood in my spit is now very light and i only see it from time to time not always. i feel mucus in my throat and took a medication called mucuslovan and strepsils , and its getting cleared up. i feel like something is dripping from the back of my nose to my throat from time to time and my throat feels sore (a very light type of sore), but there s no blood when i blow my nose, i don t have any coughs, i dont feel any pain anywhere, i am able to swallow (food & water, hot or cold) normally. I m wondering what might i have thats causing me to spit very light blood? is it from my lungs or throat or nose?