I had brown discharge at about 9 weeks due to a prenatal exam. My doctor chose to do a pap as I would have been due at about the same time as delivery and pregnancy can cause cancer cells and such to accumulate faster...mine lasted 2-3 days and I had the strings and stuff too... it was scary, but I had been told to expect spotting. I also know people can spot after sex or other irritations of the cervix, or just in response to your changing hormones. The best advice I can give you is the same advice that my doctors gave me which is keep an eye on it. if you start filling a pad or more every hour, you start cramping, or you start with regular blood flow, go to the doctor. without knowing exactly how far along you are it is hard to know if a scan would show anything, but you can always request one and book it in either this week or next. I think they can see something as early as 5 weeks if not certainly 6 and if there is something strange happening with the pregnancy it is better to catch it early than late especially with etopic pregnancies...
Good luck