Understanding Potential Pregnancy: Timeline and Symptoms

Question
Hi Catherine.
On September 27th and 29th I had sexual intercourse with someone after my boyfriend and I broke up for a month and some. We didn't use protection but he did not ejaculate in me. On October 7th and 8th, I had sex with my boyfriend and he ejaculated in me. I took the plan b and  got my period October 12th. However, that period was really weird. The blood was extremely dark, and there were mainly blood clots. It wasn't even really blood, more like mucas. But the cramps were still there. I then had sex on the 23rd and 24th of October and when my period was to come on November 8th, it didn't. I went to the docs nov 13th and they told me I was pregnant. I did an ultra sound on january 3rd to see how far along I am, and they said the baby measures from crown to rump at 5.7cm. They also said the baby was at 12W 2D at that moment. I am confused and I don't know who has fathered my child? Please help me as I am worries everyday and can't relax for the sake of this baby

Answer
Based on your ultrasound, you most likely conceived around Oct. 23rd, which means that your boyfriend is the father.  There is absolutely no way that you conceived in September or you would be a month further along than you are, which could not be missed on an ultrasound.