Overthinking/paranoid...please help!

[Stacey1989]

Im currently 40+4 days pregnant and im driving myself crazy about something that probly isnt even possible. Heres the situation:
A few years back i was told i had pcos so my periods have never been regular, sometimes going 2 months without a period and then having two in a month kind of thing.
I was with a man for a while and had sex with him for the last time on the 23rd september 2015, the next day i had a period so didnt think anything of it. 5 weeks later i had sex with another man on 27th and 28th october 2015. I found out i was pregnant on the 26th november 2015 and because of a bleed i had an ultrasound on the 28th. The crl of baby said that i was 5w6days with a due date of 24th july 2016. I had another scan for the same issue at about 6w4days and that came up with the same due date.
My next ultrasound was on the 12th jan 2016 and baby measuresed at 12w5days witch gave a due date of 21st july 2016. Only 3 days difference so this didnt bother me.
Ive recently been thinking that because of my irregular periods and the fact that when i ovulate is a total mystery that maybe the ultrasound is wrong and that it is the first mans baby. When i foumd out i was pregnant the first man didnt even cross my mind so i told my partner about the baby. It probly all sounds straight forward to you and i think the reason im being so paranoid is because the first man is a black man so if it is his everyone and my partner are going to think ive been lieing to them the whole way through the pregnancy!
So my questions basically are:
Can the 6 week ultrasound be off by that much? 5 weeks?
Does my irregular periods effect the 'missing two weeks' of pregnancy at the begining? ie: gestationa age vs fetal age?
With the dates and info i have given you what do u think? Am i just overthinking it all?
Thank you

[FellOutOfBed2wice]

I think it's basically impossible to be as pregnant as you'd be with the September conception date. I know I conceived my DD on October 15th (was using ovulation sticks and the clear blue machine) and she was born at 40+1 on July 5th. Therefore you'd surely be about 45 weeks pregnant by now and whilst it's not impossible it seems like it would be borderline a one off rarity.

[quitecrunchy]

No it definitely sounds like the baby is bloke #2's, worry not! Good luck with the birth.

[EreniTheFrog]

Agree with crunchy - it will be #2's. Even if you hadn't had any scans, it almost certainly would.

Hang in there, please. It's such an anxious time, I know.

[Stacey1989]

Thank you for replying every1. I cant believe how paranoid im being! Deep down i know that its my partners but every now and then i get a feeling of dread thinkinh what if! I want this baby more then anything so just want everything to be perfect