Right now the encounter is 10 months ago. Trust me, a person who has had 2 kids, that you would definitely know if you were pregnant. You are not. I can't say why you have fixated on this particular thought but I can say that if you seek the help of a psychologist they can help you figure out why you are stuck on this thought and teach you how to stop the cycle of irrational thinking. Are you going out and buying birth control tests as part of this problem?