What Causes Early Menstruation With Lower Backache?

Hi, I have a usually regulations 28 day cycle . Ten days after I should've been ovulating and did have unprotected intercourse, practicing the pull out method which he's always sure would work. Eleventh days after I thought I was on my period but right away noticed it wasn't normal and flowing. I assumed it was my period but it was 7 days too early. I did have light cramps, lower backache , increase in appetite , and really sentimental but no tenderness or breast pain . It's been four days since my light period* or possibly implantation bleeding. Could I be pregnant and how accurately would a home pregnancy test be right about now?