what does this mean?

I am really in a confused state. Me and my boyfriend have a sex very often and I had sex with my boyfriend a week after my period and the next day my period started again. I took it as normal because I thought a lot of women have their period next day after having sex due to the remains and for me the period lasted for 5 days, which I thought it was normal. Exactly after a week we had sex again and i had my period again! I don't know if this is normal, because from what I know a menstrual period occurs every 28 days, and I had my period twice within the 28 day time frame. What does this mean? does this mean I am pregnant?