My period is super-light... why?

So I'm 16, and even though I've been having my period since I was 13, they still haven't regulated. I usually only get one every 2-4 months, and when I do it's really really light. Like a few days ago i saw a bit of red so I've been wearing pads, but after that tiny redness only a little has actually come out.. This is often the case. Am I excersizing too much? (I run for about 30 minutes a day) Am I too fat? (5'1, 103 lbs) I'm sooo confused..My period is super-light... why?
your not fat you may not have regulated yet you hae to see a doctor if your worried sometims if you have light periods it can aslo have to do genetics
no your just one of the lucky few
when I read the ? I thought I wish I were that lucky. Now that I see your age it is normal not to be regular in teen years. Girl don't knock it some of us have the opposite problem if one could call it that.