is it possible I'm pregnant?

A guy came inside me on the 22nd of September.  I was already late on my period (my period is pretty normal but abnormal at times too so it didnt raise concern because I knew I wasn't pregnant).  I think I may be now after the unprotected sex.  When this happened I didn't receive what I thought to be my period until like around 14 days after the unprotected sex.  I figured it to be my period because it started light and got to it's usual heaviness.  But it only lasted for bout 4 days when it usually lasts around 6.  It stopped abruptly. I'm planning on getting a test tomorrow.  But just wanted to know if this sounds common.