CONFUSED!!!

SO CONFUSED!  My LMP was 21/07/2011 ( i usually have a cycle every 26 days although some months i do only have a break from bleeding for just over a week) I did something really stupid and slept with a ex boyfriend the weekend after my LMP (around the 30th july).
The following week from the 7th August up to 12th myself and my partner had sex 3 times. My period was due on the 15th August on the 12th I began to get cramps like i was about to begin my period, my period never began although i continued with these cramps.
I decided to do a pregnancy test 20/07/2011 and yes I am pregnant!
On the 21st I had a blood test done my hcg levels were 1027 i had them repeated the 23rd they were 3025 ( doubling every 29 hours)
So first question is would they have doubled at that rate (every 29 hours) from conception ? If so this would clarify the period pain i thought i was getting two days before i was due as inplantation (implantation) cramps.
I was In California at the time of all of this ...
So question 2 could i have ovulated later what with the time difference ?
I was also taking Antihistamines roughly from when my period ended right through
Today I had a scan and it showed I am 6 weeks pregnant this does fit in with my LMP all but one day as Im actually 5weeks and 5 days
So my final question is would the scan bring up the same amount of week regardless of when I ovulated?
I had a scan today and was told I was six weeks pregnant and yes from my LMP it is exact to the day

Anyone that can shed a little light I would be so very grateful
Thank you

[bhenneker]

First Day of Last Menstrual Period:  July 21, 2011

Probable Date of Ovulation:  August 4, 2011

Possible Dates of Conception:  July 31 to August 8, 2011

Due Date:  April 26, 2012 (40 weeks)

they dates are way to close to tell it could be either your ex or the boyfriend

[MissTee00]

Thank you bhenneker for your input