don't know if I got pregnant before my period

[I'mgaj]

I'm very confused about when I got pregnant. I had sex with a guy on Aug.25 and he (pulled out). I also had sex with my boyfriend that last week of Aug.  On Sept. 2 I started my period. After 3 days of my period I continued to have sex with my boyfried. I missed my period in Oct. and found out I am pregnant. On Nov.1 I had an ultrasound done. The ultrasound said I was 8 weeks and 6 days pregnant and the baby measured avg. 23mm.  I would like to know how accurate the ultrasound is along with the measurements.
If I got pregnant before my last period, then I was really 9 to 10 weeks pregnant. But If I got pregnant after my last period then I would only be about 7 weeks because of ovulation,right? The doctor said I was 8 weeks 5days pregant according to the first day of my last period. When did I really get pregnant before or after my last period? If it was before, could I have been 9 weeks 5 days at the time the ultrasound said 8 weeks and 6days or could I have been less than 8weeks pregnant.
I'm sorry for the confussion but If you could please help, I would greatly appreciate it. My boyfried is so excited, and I realy screwed up by being with that other guy.

[AnnieBrooke]

Hi, Kkaattee, please write it out for me like this.  Check what I wrote, also, to be sure I'm understanding what you are saying.  You could have had sex with your boyfriend as close to the sex with the other guy as July 23?

First day of last period:  July 5
Sex with boyfriend:  July __ - 23
Sex with other guy:  July 24, 25
No sex with boyfriend:  July 24 - 30
Sex with boyfriend:  July 31 forward

Had ultrasound on (date) and was told I was __ weeks __ days along
Estimated due date given to me by ultrasound:  April ___, 2016

[Kkaattee]

I had sex with my bf anytime before aug24 I'm not quite sure but I do almost all the time and I just know the days we didn't which was 24,25,26,27,28,30 all the time before that and after on the 31 I can't really give you dates because I don't keep track but we've had sex. Is it possible it can be his. Honestly what I don't get is if they give you and ultrasound date is the egg already there the two weeks prior of when the baby start forming. Thanks a lot for you help.

[AnnieBrooke]

If you got the 7 weeks 4 days figure from an ultrasound, it would suggest the other guy is the dad, especially if you didn't have sex with your boyfriend around the week of July 20 because of the fight.  If it just came from a calendar or little wheel, there might be some chance it's from your boyfriend, depending on when you had sex with him.

[Kkaattee]

If i been having sex with the same person for 4 years I took out my iud 4 months ago I'm 7 weeks and 4 day I had a fight with my boyfriend and had sex with someone else July 24 and 25 my last first day of my period was July 5 could it be his or my bf I never use protection with my bf and neither did I with the other guy.

[AnnieBrooke]

If your next period was only due around now, it was too early to test two weeks ago.

[mary_gzz]

i have already took two about 2 weeks ago and gotten a negative result on both. Could it be possible it was to early?