It sounds like your current boyfriend. What makes you wonder?
Also, when you say "then for my screening date," do you mean, when you got an ultrasound at some point? And by using the word "screening," do you mean one that is rather late, like an 18th-week ultrasound? When was the ultrasound (date on the calendar)? I ask because you sound like you think the ultrasound was using the last day of your period to determine things. But it won't do that. If the ultrasound was after your 12th week, it isn't unusual for there to be a discrepancy between dates according to the ultrasound, and the weeks according to a woman's last period. Babies can grow faster or slower than average, and by the time a woman is full term, the dates an ultrasound gives from the baby's measurements can be a full three weeks off what they are according to her last period.
It was done September 5th,... and it makes me wonder cause I heard that semen stays alive for 5 days but then again thinking about it you may be right too which I was thinking the same but since this guy is stalking and continues to bother me I wanna know if I’ll be wrong for doing a dna test
It sounds like the ultrasound was in your 20th or 21st week? So far along in pregnancy, ultrasounds don't always match when your last period was.
If the last time you slept with the other guy was the first day of your period, it doesn't sound like you need to worry about the length of time sperm stays alive in the woman's body; it would not have stayed alive long enough to be still there when you ovulated if most of your period came after you had sex.
I don't think there is anything wrong with doing a DNA test, either. It will show your boyfriend as the dad, from everything you have said here.
The way I read your post, your last period was April 14th-20th. That would make likely ovulation April 28th (on a 28 day cycle) with the boyfriend's sperm still live and kicking inside you. Sex on the day before your period begins will not get you pregnant.