I remember working with someone who had lovely dark curly hair (curlier than mine) and she said her hair was not curly until she had her kids. (I think it was wavy though, but it became very tight curls)
Me and my siblings (4 out of 5) had our hair turn curly when we hit puberty. It didnt seem to change much with pregnancy for me and my sister though, but I do know hormones do change the texture of the hair.
Hair texture is determined by the hair follicles, how they are shaped so it is not the condition of your hair itself, but the roots they come from, if that makes sense. (I read a book for curly hair a long time ago.)
You probably will have these nice waves for the rest of your motherhood. Maybe it'll change again when you go gray?? (My mom said her gray hair is thicker & straighter than the rest of her "normal" hair.)
There are a lot of products out there, each person is different but I personally prefer Frizzease styling products and Aussie 3 Minute Miracle conditioner. I also love the little tubes that come in red box Placenta Hair Repair???? they make my hair nice and managable when they start to not respond to my daily routine. Best of luck finding stuff that works for your hair! I do have a bunch of bottles of stuff I tried and dont like :( Too bad we can't trade these around...