Spotting at 6w2d

Is this normal? I feel "achy" in my lower abdomen.. like AF is about to show. I'm currently 6w2d pregnant and I don't have an appointment with my OB till the 31st. I had my HCG checked 2 times earlier this month around when I missed my period and it was doubling every 33hours. I've had no spotting or anything till now. Started last night.. and getting darker today. It's only been brown.. no red. I had a miscarriage at 12weeks back in May and had zero signs. So I'm confused... Should i go to the ER?