Brown spotting is old blood. As long as it isn't bright red, you should be fine. Still contact the doctor. If u don't have one yet, an er visit may be best to put your mind at ease.
I experienced the same thing at 9 weeks. I went to the ER and the baby was fine. It was old blood and they stated that I should only worry if it was bright red. I am currently 22wks and baby is still fine. I would just bring it to your doctors attention and let them check you out. But don't worry I believe everything is fine