On & off spotting??

Nia

My last period started on 07/06 it was pretty much light for the most part. Only one day where it got heavy w/ blood clots. It only lasted about 3-4 days. A usual period for me last up to 6-7 (28 day cycle). Me and my boyfriend do have unprotected sex.. all the time (ttc). We did have sex on the third day of my period because it was so light and I actually thought I was off. We also had sex on 07/17 and he came inside me then (tmi sorry). According to ovulation calendars my fertile window started on the 15th and should end on the 20th. But ever since the 18th I've had light bleeding. I've never experienced ovulation bleeding a day in my life and would expect it to last this long. Has anyone else ever experienced this and had a successful pregnancy?