CM, I had brown blood at 6 weeks with DS1. It was a blood clot in the uterus lining breaking away - very common apparently and harmless for the baby. I had light, brown bleeding for a few days then all was good. The day it started I went for a scan because I was so scared and saw the hb for the first time. DS1 is now 5 1/2 btw. I know it's worrying, and it would be a good idea to see your medico on Monday for peace of mind, but when it happened to me they said that brown blood is usually not a problem.