For the past 4 months, my periods have been really weird.. I'm 15, and my periods have always been medium (normal bleeding 5 days). But for the past 4 months my periods have been really REALLY light, like I could wear a panty liner for the WHOLE day and there would be little to NO blood (period lasts 3 days). I thought I was pregnant by the second month but I took a pregnancy test and it popped up negative. Does anyone knows what this is?!??!