Blood in mucus in morning?

Hey i am 23 years old...smoked on and off for the past 4 years mostly on weekends at parties, my question is this...i recently had bronchitis and waited over a week and half before i went to see a doc (was a cough at first but got worse) the doc took blood sample from me and chest x-rays - the blood test came back for over 18 different things cancer cells cholesterol etc. the chest x-ray came back neg for pneumonia i did have bronchitis but i was also coughing up streaks of blood in my mucus i told my doc and he ured me it was from me coughing a lot and waiting over a week to see him, its been almost 2 weeks now and I'm still coughing up small amounts of blood in my mucus in the morning but goes away after 10-15 minutes after waking up......i just would like to see if there is any other causes to this or if i might have cut my throat or bronchial tubes from coughing so much also my mucus is not dis colored any longer so if anyone has any answers or why this might be happening i would appreciate the feed back - thanks -