Yes congratulations you are definately pregnant. I am currently five months pregnant with my fourth baby and the same thing happened to me each time. If its light it just means your only just pregnant. Most likely a couple of weeks give or take. I even rang the consumer number on the pregnancy test information leaflet to be sure and they said definately yes and i was (four times now.) congrats. The lighter it is the earlier your pregnancy is as it works on the amount of hormone in your urine.
A faint positive is usually a positive! I got a faint positive 5 days before my missed period, and the next morning I took two more to be sure, and they were much darker. Take another test in the a.m. or wait another day...but its probably true...you are pregnant. Good luck!