Paternity Test

Don’t judge please ! So I’m kind of feeling torn about what to do. I’m currently 13 weeks today & I’m really thinking of getting a paternity test. I always kept track of my periods & when I had sex, but this time was different Bec I started BC for the first time in my life which was in May. I had sex w my ex May 8th & started my period May 9th. Me & the guy I had been seeing for a while had sex about 3 weeks after my period ended but I had been taking BC the entire time. I had my first ultrasound on July 11th measuring at 8wks & 5days (9wks going by LMP). & I know it’s possible to get pregnant while on your period if it’s irregular. What do you guys think ?