Every morning for a few months, I always spit up some yellow phlegm . I do not smoke , I am a teenager, overweight , but eating better. I do eat junk food often, but balanced with fruit and veggies. I read that this could be the cause of excessive yellow phlegm? Could smelling or brething in a second hand smoke, moldy food, or other thing like that have caused something? The phlegm is never bloody.