hi mariaberthiaume, yellowish or greenish sputum or phlegm could mean that you have some sort of bacterial infection and if an antibiotic course has not cured you then either you have not taken the full course or not recevied the antibiotic you are sensitve to. Aslo if you are a smoker you need to stop smoking.You nneed to get a culture and senstivity of the sputum and take a course of antibiotic that the organism is sensitive to You also need to take an xray of your sinusus to see whether you are suffering from sinusitis. You need to get to the bottom of the problem and get the appropriate treatment. Do not ignore it.

Hi welcome to Health care magic forum. It could be sinusitis, or silent tuberculosis laryngitis, etc. You did't mention whether it is subsiding in between when you use medicines, if there is relief and recurence it could be allergic rhinitis, or eosinophelia etc.
I advise you to consult an ENT surgeon for diagnosis and treatment. You may need to get sputum for AFB, MRI, along with other routine tests for confermation. if allergic try to find out when you are getting the attack more after taking some foods or after using some things like spray, powder, soap, etc which you use sparingly.
Besides i advise you to follow some diet recomendations as Avoid taking icecream, icewater, cooldrinks, fruits, juices and seafoods to which you feel allergic.
Take more of green leafy vegetables, pulses, sprouts, milk, egg to improve blood , general health welbeing feeling, and resistance to fight infections. Wishing for a quick recovery, and thanks for calling.