What Causes Stomach Cramps And Heavy Vaginal Bleeding?

Serious question been on the depo shot for almost 5 years now and I did not get my period Yesterday I got it. I have not had my depo shot since April waiting for new insurance I woke up this morning bleeding everywhere it was running down my legs and big amounts on my kitchen floor to the bathroom from just walking the bleeding has not slowed down at all I have bad cramps I m wearing super tampons and changing them ever 15-30mins should I be worried