Question about on and off brown spotting during early pregnancy?

Hi, 2 days after I got my BFP i spotted. Then about 4 days later a little spotting and now on and off every few days or so. It is brown to pinkish and only when I wipe. I have had no cramps or enough blood to even get on my panties. However, I am almost 7 weeks and the only symptoms I have had are slight tenderness in the and am pretty tired. Of course I am wondering if I am even pregnant, I have tested several times and they are still positive. Will get my first u/s next week. What are the chances there will be nothing there? Worried...