My periods have always lasted a full 7 days. All my life my periods have been in the medium/heavy flow. I'll be 21 soon and within the last couple of months, my periods have become EXTREMELY light. Like I could wear one tampon all day and it still wouldn't be full. And I use to cramp like crazy the first few days of my period and now there's nothing. I'm not only birth control or anything.. Is this normal or not?