Brown spotting

Has anyone ever experienced brown spotting in early pregnancy? I'm 5 weeks, 3 days and I started spotting a little yesterday and it has continued on through today, and is making me very nervous!! It doesn't soak through a pad, but it's noticeable. I'm not cramping but my back hurts (tho it has been hurting since day one). I looked online and some sites say it's totally normal, but others say to call the doctor right away--I just am not sure what to do!! Any advice would be helpful--my first appointment isn't till October 13 :(