What Does Bleeding With Painful Cramp Indicate?

Hello. Im concerned about my menstrual cycle. I was on depo for about 9 months. My last shot was due in September. I haven't had a period until yesterday. I bled through two regular tampons yesterday during the day. Then after about 5 hrs of sleep (with regular tampon) I woke up soaked in blood with really painful cramping. How concerned should I be? Should I see a doctor? Is this normal?