Spotting on day 18

I was just wondering if any of you have ever had this. Im usually spot on on my period which is 28day cycle. For the first time in my life I have brown discharge on day 18. It feels like a light period but it's 10 days early. According to the calendar I just finished ovulating 3 to 4 days ago. I'm just wondering if anyone has ever had this and if so what it could be. Thank you in advance