started period night of unprotected sex preagnant?

I got off of the BC all together because I was having way to many break through bleeding and all in al I just didn't like all the added hormones in my body... to many issues. So I schedueled an appointment with my OBGYN to be fitted for a dyaphram but have been waiting for a while to get an appointment. So the boyfriend and I have resorted back to the old withdraw method. On Thursday the 16th we were both drinking and I think he just got carried away and decided to go inside me. I started my period that night. The next morning we did it again and he pulled out but said he thinks he went a little inside me again. I didn't take a plan B pill but got 2 of my sisters BC and took one around 2am Saturday morning then another one at 2pm the same day. The doctor put an order in for a blood test and said I can come in when I am ready to take the blood test. She also put me on pre natals just incase. I wanted to wait until I got closer to my period before I test so I would be sure. I have had a lot of frequent urination but I kind of allways been that way. I have also been having a lot of headachs that seem to come and go. I have had very slight cramping but nothing like when I am on my period. My cramps were really bad the first couple of days on my period, and my period only lasted 4 days and was heavy the first day then was really light the last 3 days. I noticed some very light brown spotting but I am not sure... it was pretty faint. I have thought I was pregnant in the past and have been dissapointed so I am trying not to get excited to soon when it could be false. I know there is a slim chance that you can get pregnant when you are on your period but what are the chances? What is the ratio? Could I be pregnant?