Periods, embaressing subject but need help!!!?

Ok, I'm 13 years old. I hit puberty when I was about 10, got hair like on my armpits at age 11 and hair 'down there' at like 10. My boobs have recently gone up a cup size, in like the space of a week or something!:S I have been having like gallons of discharge(clear and no odour). My tummy has been hurting horribly. The pain is in my lower stumach, and lasts for about an hour each day. I keep getting headaches, feel sick, in pain. I've took tablets but they don't do much. I heard that these are signs of your period starting? Is this true?? And when do you reckon they will come as I need to be prepared. What do I need to carry with me when I'm at school incase my periods start? What do I say when they do? Help please, i'm a bit scared haha!!xx