Period confusion

Has it happened to anyone else where you get your period buts there is no blood and it's just mini clots... this just recently happened.. it started out with a large palm size clot and then just little ones after, doesn't even fill a tampon or a pad and I'm not sure if it's because of my birth control or what... I have an appointment with my OB but I'm wondering if it's normal or has happened to any one else.