Hi , My Son Is 6.5 Yrs Old And Is

Hi ,

My son is 6.5 yrs old and is having a runny nose for close to a year now. In the beginning it was accompanied by worst cough for around 6 months but now subsided. Currently he has a very mild dry cough intermittently. Sneezes once in a while but has a non stop runny nose.there were hardly a few days when he didn't have runny nose. The phlegm is very clear and colourless. Is this treatable and curable? What are the complication if left untreated.