morning after pill?

I took the plan B pill two fridays ( December 2)  ago after unprotected sex (he didn't come in me but just to be on the safe side I took it, I was also on my period) and this past Tuesday (December 6)  I felt super nauseous and I had a horrible headache. That next day I noticed a brownish/red bloody spot in my undies. But that was it, I wasn't bleeding anymore. (Super strange because I don't spot often) and since then I've still had very bad headaches, moody, and I get nauseous. Are these pregnancy symptoms or side effects from the pill?