Found out recently I was pregnant. I had sex with one partner about the days before I was supposed to ovulate and sex a one night stand on my ovulation day. I had an ultrasound vaginal one that measured the sac saying I was 5 weeks 6 days and that's longer than Ive known the one night stand Guy but that also puts me as having my period while pregnant even when they estimated from first day of last period they said I was about 4 weeks and some days that's still longer than I've known the one night stand Guy so am I freaking out for nothing is there no way it could be the one night stand even if I had sex with him on ovulation day? Is it definitely my regular partner since both estimates were longer than I've even known the one night Guy? Please help

Impossible to tell at this stage due to the timing of the encounters.
The ONLY sure fire method to determined paternity would be a DNA test involving all parties AFTER the birth.

Do you know how accurate ultrasounds are?

Impossible to tell at this stage due to the timing of the encounters.
The ONLY sure fire method to determined paternity would be a DNA test involving all parties AFTER the birth. Do you know how accurate ultrasounds are?

NOT accurate enough to determine paternity.
Gestational Dating is all Best Guess based on available evidence.