Post ovulation preAF bleeding

Megan
My ovulation window ended last Thursday, I sad sex on Saturday and today I was bleeding when I went to the bathroom. 
Back up to a month ago. SO and I had sex three days during ovulation, AF was 4 days late and when it started it was shorter than normal. 4 days instead of 6-7 with super thick clots. Making me think that it was a failed implantation. Fast forward to missing the ovulation window this time. Experiencing nausea, fatigue, lower back pain, occasional pelvic pain, and slightly sore breasts/sensitive nipples. 
No idea why I'm bleeding two days after the last time I had sex and worried that it could be something worse. Planning to go to doc this week to get everything checked out.
Any ideas?