Does anyone know the name to this emotion/feeling?

Basically, it’s this REALLY strong gut feeling. It usually happens when I’m changing, in the restroom, going out(specifically sleepovers), or doing something you wouldn’t have done at a younger age. (Otherwise it also happens randomly) The common thoughts that always come to mind is the idea of growing up. How I’m going to become a Mom and have kids. It makes me not want that. It also suddenly makes me miss the past like crazy. Usually 3rd grade. (I’m rising 10th grade) But then, it’s not just another emotion, because it’s one that I hate THE MOST. It’s such a horrible feeling to have. I can usually feel it getting to me and the first thought is to try and ignore it, but I never can. I seriously bet when I get married and have sex, it’s only going to be 2 minutes of pleasure for me. Also, it’s not guilt or regret, I know what both those feels like and it’s nothing compared to it.