Understanding Early Pregnancy HCG Levels: A Detailed Explanation

Question
Im am a 25 year old woman and I have a six month old son. On November 16 2004 I took a home pregnancy test and it was positive. Ok so we know Im pregnant. I went to the doctor on Nov.18 and he performed a abdominal sonogram and saw the fetus. I had my blood drawn on the 22 of Nov. and the lab tech order the wrong hcg test so on the 24 of that month she called the lab and changed the test so it can give the levels. They were 1976.6( how many weeks does that estimate to?) On Nov. 26 of 2004 I went to the ER because I was feelin sick they performed the hcg level again and they were 8696. They also performed a sonogram that estimated me to be 5.4 weeks( whatever that means) Now my problem is I slept with 2 men. I was with one of the men(we will call him M)I was with him a lot in the month of october and the other man (we will call him D) i was with on October 31 and Nov 1. My caculation would lead me to M but could my caculations be wrong. From the time I was with D I found out I was pregnant15-16 days later. Isnt that allittle to early? and according to the hcg blood levels wouldnt I have been to far along for it to be the second man? Please help me I am so tired of racking my brain.

Answer
It would help to know the first day of your last period. HCG values have too large a range to be helpful in determining exactly when you conceived. HOwever, If a sonogram on November 26 showed you to be 5.4 weeks pregnant, your last period probably started on October 19. If you have a normal 28 day cycle, ovulation occurs on cycle day #14 and you can conceive if you have sex on cycle day #13, 14,15, or 16. Therefore, if your last period started on October 19, you could have conceived if you had sex on October 31, November 1,2, or 3. If you did become pregnant on one of those days, a pregnancy test could not have shown a positive result until 14-21 days later (which it did). Therefore,  "D" is most likely the father.