Please help!

Hello Ladies.
I had my period this month from the 4/9th which came a week early to start off with. 
I was meant to ovulate on Monday however when I woke up there was blood in my underwear it was red/brown colour. It feels like a very light period over the last 4 days however no cramping. 
I have been changing my tampon and there has been blood & mucus on the tampon but not too much. 
Any suggestions on what this could be?