Your ex sex was in prime time to catch ovulation. The chance of pregnancy from sex on CD7 is slight but definitely not zero. In view of possible fertility problems with the ex, I’m thinking there is an even chance of either being the winner. Congratulations on your first pregnancy!
You say your ovulation week was November 23-29. Do you know this from an app or from using ovulation test strips?
Have you seen a doctor and gotten an ultrasound? If so, when in the pregnancy was your first ultrasound? And what estimated due date did they give you when you had your first ultrasound?
As you know, protected sex is less likely to produce a pregnancy than unprotected sex. An "ovulation week" is not really a week long -- ovulation doesn't take a week, it takes a minute, so saying your "ovulation week" is something of a misnomer. (Your egg pops out of the ovary in a given moment in your menstrual month, and then only lasts about 24-36 hours, after which it will fade, unless it gets fertilized.) What the app is saying is that sex within that weeklong time period might produce the pregnancy. But if your egg did pop out around the 27th, the sex on the 20th was a little too early even if it had not been protected.
Over how many months did you and your ex regularly have unprotected sex and not get pregnant? It's not unusual for a couple to go a while without conceiving even when they are having a lot of sex.