Light spotting at 5 weeks

I started spotting 3 days ago when I turned 5 weeks. Nothing pink, red or stringy so far, just light brown in colour. I haven't had any pain or cramping either, but it concerns me that it hasn't gone away. I can't see a doctor until tomorrow and am so worried that it could be an early sign that I'm going to miscarry. This is my second pregnancy and I dont remember this happening the last time...Has this happened to anyone else?