What Causes Brownish Vaginal Discharge After Having Plan B?

I was wondering what this brown discharge is from my vagina. I had sex on January 16th, and the condom broke. The next day, I took the Plan B pill. Yesterday, the 25th of January, I noticed a brown discharge. My periods usually come on the 4th or 5th of every month, but it was a few days late last time. Is it from the Plan B? Could it be that I am ovulating? Is it pregnancy? Please help.