What Causes Vaginal Bleeding During Pregnancy?

I started my period on the 21st of January. It lasted till the 29th of January. I had unprotected sex on the 2nd or 3rd of Feburary. I started to bleed on the 6th of Feburary. I'm currently bleeding now. It isn't my normal period though, it is very light. My mother said she had bleeding during her whole pregnancy. Could this be true for me, could I be bleeding and be pregnant?