What could this be?

Christina • I'm 25 years old. Mommy to a 3 year old, and a 5 month old 💗 Angel baby 10/25/17 🌈
My period ended the 24th of last month. Once it ended me and my boyfriend had sex every other day on my supposed to be "fertile week" And yesterday night I had light pink discharge when I wiped them I woke up this morning and wiped again and it was blood (menstrual blood looking) what could it be? My period just ended why would it happen again? Ugh