I agree with the others. I had the same thing at about 6 weeks and it lasted for about a week. I saw my ob as I was scared about it, and she did an u/s and said it was a blood clot in the lining of the uterus that was just coming away. Apparently this is very common and causes no harm whatsoever. My DS in now 17 months so I guess she was right! All the same, if you are worried see your ob/mw for peace of mind - it beats worrying!