I used Clearblue digital ovulation kits and detected a smiley face. But after 2 days I noticed that I have brown spotting after unirated. Why is that happen? Thanks

Haylin... please do not ask the same question under different names. The answer is the same:

It could be from recent ovulation. It could be from recent sex. It could be from hormone changes.

If you are wondering if it might be due to pregnancy, it wouldn't be, as such. If you did happen to become pregnant that recently, it would take roughly a week, perhaps a bit more, before implantation would be complete.