Possible Paternity: Understanding Pregnancy After Intercourse

Question
I'm 20, I have no children, and the first day of my last cycle was Oct. 31. My boyfriend and I were fighting and I went to a previous lover and we had sex. He did not ejaculate in me, but I know that there is pre-cum. This was the day after my period ended. My boyfriend and I did not have sex the next day, but continued to have sex on a regular basis thereafter. I am now 5 1/2 months pregnant and my fiance is in Iraq and I dont know how likely it is that it is the other guys. My fiance has no idea. I usually had a normal cycle, about 30 days.

Answer
If you normally have a 30 day cycle (from the first day of your period until the first day of your next period) ovulation occurs on cycle day #16. If your last period started on October 31, you would have ovulated on November 13 and could ONLY have conceived if you had unprotected sex on November 12,13,14, or 15. You should therefore be due on August 6. I assume that your period is not that long and the day after your period ended was before November 12. Don't worry.