I didn't receive the shot before getting pregnant, and I'm just wondering if my body is going to build up antibodies, when does this occur? You do not need the shot before you are pregnant. Your blood will not build up the antibodies.
If I am RH negative, wouldn't my mother have had to be RH negative as well? If so, why was she never informed of this when I or any of her children were born. No. That does not mean she had to be Rh-. Rh- is recessive which means that each of your parents and the Rh- gene underlying their dominant Rh+ gene. The two recessive Rh- genes met up to make you, Rh-. Because your mom is Rh+ she never had to worry about the shot.
In addition, any woman who is Rh- with a partner who is Rh+ will have to have the shot in case there is fetal Rh incompatibility. I hope this helps.