What Causes Scanty And Brown Colored Menstrual Period?

im 15 and i usually have an irregular cycle and its about time to get my period and it is usually a medium amount of blood. this time i have really thin and light brown discharge. is this normal? is it my period? its been happening for 2 days now. also i fooled arund in a hot tub with a guy about 5 days ago we didnt have sex but he ended up ejaculating is it possible that i am pregnant?