Mine did this too, just before my 49th birthday I got a sex drive for the first time. I'd always had sex and always had the ability to cum and therefore enjoy it, never really wanted to though, a bar of chocolate was far better, I'd no inclination to get naked unless I wanted a baby then I wanted to for the obvious reason of getting pregnant.
I turned into a total nympho, wanting it 3 or 4 times a day, sending my husband pictures of my underwear at work, he thought all his christmases came at once and while it eased off after the first three years, it's still a sex drive and my husband still loves me having one.
It isn't talked about a lot, I guess noone wants to hear about horny old women, not what men want to hear I mean.
I was thoroughly annoyed that people assumed I wanted sex all the time while pregnant, the way pregnant women are supposed to, definitely not me, I felt sick, besides it doesn't even make sense for a pregnant woman to want more sex.
Understanding why mother nature might prompt you to have one more child at the end of your fertility is far easier to grasp.