Coughing up bloody phlegm!!! help?

Well its ben about a month now and it feels like theres mucus in my chest and lower throught so i clear it and i get mucus with blood in it its light colored with light blood.. mind you that i have no cough or been sick.. i'm only 20.... i smoke on occasion i dont buy just bum cigs lol but not often maybe 2 or 3 a week .. i also run close to 25 miles a week and i am in very athletic shape i honestly dont know what its from and i'm a lil worryed..