What Causes Brownish And Pink Discharges?

My last period was Nov 21, and it lasted for 4 days (the normal for me, but my period was also 4days late this month) I woke up this morning and when i peed there was brownish blood on the toliot paper. As the day progressed it became light pink. I have light pain in my lower abs and in my back. I also have a light headache and everytime i eat i just want to throw up. I also feel extremely weak.. what could this be?