I had this last week when i was 6 weeks. Panicked me too. I called NHS Direct and spoke to a nurse there, She said that as long as there wasn't enough to soak a pad, it turned pink or red or was accompanied by abdominal pain then i shouldn't worry. Aparantly it is quite normal. The nurse thought it could be left over from implantation.
If you are worried call your doctor to put your mind at rest, but everything should be fine.
