Whose baby😐?

Last year, july 3rd I had a one night stand with a guy. Got my regular 5 day period 3 days later.

July 22nd I went to my gynecologist bc I was having weird discharge. Turns out the guy gave me chlamydia. He also done a pregnancy test on me and it was negative. (If I would have got pregnant from July 3rd would I have had a positive pregnancy test yet if I was pregnant??)

July 29th me and my current bf got together and the same week I started another 5 day period.

August 21st I went to my gynecologist again bc I just felt off. He ran a pregnancy test and it was positive! They done an ultrasound and there was no sac or baby found. (Would there already be a baby on the ultrasound and sac if the baby was from July 3rd??)

Is there any way possible my baby is from the one night stand from July 3rd?? My baby is already here his due date was April 28th of this year.

(We are getting a dna test done next week and I am freaking out!! So pls help a girl out!!)