I can't sleep with worry!

I need hElp! I just can't seem stop worrying and it's killing me! Me and my partner split for about 6 weeks and I made the very drunken mistake of having sex with some1 else! My last period was on 6th September and I slept with guy A on 17th although I don't remember much about it and then I got back with my partner a few days later and we were then having sex every few days. On 14th October I did a clear blue conception indicator pregnancy test which said I was 1-2 weeks, I then had a blood test on 15th October and my hcg levels were 127, two days later they were 290 and another 2 days later they were 690. On 26th October I had an early scan and was told I was 5 weeks 4 days . 1 week later (2nd november) I had another scan and was told I was 6 weeks 4 days. Then I had my dating scan on 22nd December was told I was 13 weeks 5 days and was given a due date of 23rd June based on the baby's head circumference. I would really appreciate advice on when I concieved as this is eating me alive! Thank you