Which one is the father

So me and my ex had sex and then 6 days later, I had sex with another dude. I know I should’ve used protection my dad died and I was being careless. So the 14th I had sex with my ex( guy a )and 20th with (guy b ) and I was supposed to get my period but didn’t. I tested a few weeks later and was pregnant. I went to my ultrasound and I was 7ish weeks ? But I don’t know which one is the father since they are so close.