it seems like your ovulation date would be closer to feb 26-28th, so i would say it is your husbands baby.
but sometimes because of stress, and other things that can throw our ovulation off a little bit.
i would be surprised if your ex is the father because a week after you had sex with him your period would be do.
have you talked to a doctor about this?
i had a friend who went through the same thing and the ultrasound was in between both men, making it impossible to figure out who is the dad.

Hun i am in the same pickle you are..
Me and my boyfriend have been together for a while,but he broke up with me in Feb so i got back with my old ex. We had sex Feb.10
Then later i got back with my original boyfriend and had sex March 2-8
My due date is Nov.20

I used the due date calculator to see and it said that if it was the exex(lol) i would be due nov.3..
and if it was my boyfriends im due Nov.23..

the 23 is closer to the 20th so i hope its my boyfriend.
so by the sound of it...

IT SOUNDS LIKE YOUR HUSBANDS!
but i cant be to sure babe cuz there not always certin.
I will pray for you women! hopefully you can pray for me too <3