When did I conceive?

Hello. I made a mistake and am now in an unfortunate situation. I will try to give you the shortest summary possible. My fiance and I were having relationship problems over his changing his mind about whether or not he wants children. He has changed his mind several times over the years and finally decided he did and so we moved forward with wedding plans. However, he changed his mind again and we had a temporary parting of ways. During this time, I slept with a former boyfriend. My fiance and I reconciled. Two weeks later I found out I was pregnant. I was happy at first. The "date" with the former boyfriend was shortly after my cycle and not near my ovulation time so I initially thought nothing of it and then anxiety hit me and my mind is completely out of sorts. If sperm really live 7-10 days, then I may have a problem. I have done research on the possibilities, the egg's life, average sperm, tracked back days and my exact ovulation time, menstrual cycle dates, etc. (I had tracked this on a calendar for 6 months). I usually have 28 day cycles, if not, then that month is 29 days, luteal of 14. I have consistently had ovulation symptoms on day 14 of my cycle and usually ovulate that day or the next day.

Following are the relevant dates:
May 12th - menstrual cycle began (last 4.5 days)
May 18 - saw former boyfriend
23 & 24 - reconciled with fiance (relations on both days) (Day 12 of my cycle)
25th - first sign of ovulation symptoms (Day 14 of my cycle)
26th-ovulation symptoms (prob ovulation date, Day 15 of my cycle)

June 2 : 7 days past ovulation date began experiencing implantation spotting 5 days in a row

June 6: took an early preg test on the 6th (Day 26 of my cycle, just to see, it was neg)
June 7: took another EPT, neg
June 8: took another EPT, neg (this was day 28 of my cycle)

June 9: went to doctor, had urine preg test = neg (day 29 of my cycle), however, had them due blood test and they called me next day to say it was positive, HCG Level 50. The level was really low and they said it may be extremely early in your pregnancy but because of the low number we need to make sure the # is increasing, went back 48 hours later and the HCG level was a 144

Thank you for your time.