Blood in my phlegm? Lung cancer?

I started smoking about 5 years ago when I was 15, I've been smoking almost non stop ever since, in the last year I've been smoking more than ever- at least one every hour, sometimes half an hour. However I went away to stay with my friend last week and had no ciggarettes for 3 days, then when I came home I started again! Last night my throat became quite sore and this morning when I woke up I had some phlegm in my throat with a very faint streak of blood in it, I thought nothing of it but its happened four times this morning, just a small thin streak of blood. I looked it up on google and the first thing hat came up is lung cancer. Call me paranoid but I keep thinking I might have it, I know I'm only young (21) but I really havn't taken care of myself for a long time and I'm wondering if not smoking for 3 days and then smoking so much straight away has caused something horribble. What are the chances of me having lung cancer? I havn't been coughing and I havn't had a cold or a mouth injury, so why blood? If a real doctor could answer my question I'd really appreciate it.