What Causes Abdominal Cramps,back Pain And Brown Discharge During Pregnancy?

Hi, I have a dr appointment tomorrow but I'm cramping and have back pain with brown discharge, with my first pregnancy I had that and I know it's old blood and then today I had a grayish discharge with all my symptoms should I be worried? I know I'm at least 8 weeks no more then 12 weeks pregnant. Any advise would help