Having Chest Cold,tonsillitis And Bronchitis With Green Phlegm From Last 7 Years

Every year for at least the last seven years I tend to get what seems like a really bad chest cold - however they often last for 1-2 months. I usually end up going to the doctor 3-4 times trying different types of cold meds. This year it started with what the doctor said was the flu , and then a chest cold, then tonsillitis , and now bronchitis . I am still coughing up green phlegm , coughing and blowing my nose non-stop (it is both clear and greenish-yellow in colour). And my body is very very weak in energy and I am having trouble breathing. Why does this happen at least once a year and is there anything that I can to do prevent it from happening in the future? What is it exactly that I am dealing with and why does it stay so long?