Can I be pregnant?

I was pregnant on November 14 and I had a miscarriage at about 7 weeks or so. On December 25, 14 was when I miscarried. I had sex with my partner a week later, used condom but it came off and was left inside me. He noticed. Can that cause a pregnancy? I should of have gotten my period by now but I missed the day. When I miscarried, I been told if I was to take a home pregnancy test it would still come positive. So what should I do?