Pregnancy after MC?

Okay guys, I had a miscarriage at 6 wks on 9/23. Which is 3 weeks and 3 days ago. We started having sex again exactly a week after the mc, of course after all bleeding had stopped. We haven't been preventing but not trying either but I do know on one occasion he did come in me a little bit. For the past 4 days I have had absolutely horrid lower back pain. October 13th was around when I was scheduled to start my period but obviously I know they can be a little wacky after having a mc. How likely is it that I could be pregnant?