What Is The Possibility Of Normal Periods During Pregnancy?

My fiance and I had sexual intercourses in November 2010 twice while he was visiting. We didn't use any contraceptive methods. In december I missed my period (my cycle is usually irregular) but it came again in January, February, March and April on regular basis. This May I haven't had my period and I am late by 8 days. Last time I had intercourse with my fiance was in November 2011. I also noticed that I have gained weight. Is it possible to be pregnant and still get your period regularly?