AITA for not being honest about my past?

When I was a teenager I was in a very toxic relationship and ended up ”pregnant”. By pregnant I mean it was a phantom pregnancy and for whatever reason my body was convinced I was pregnant even though ultra sound techs confirmed the egg was never fertilized. I eventually moved on from that guy and found my person. When talking to my mom about how serious we were getting she strongly urged me to tell him all about my past with my ex and to be honest about my ”pregnancy”, to which I told her it’s my buisness alone wether I tell him or not and now she’s telling me I’m a horrible person for keeping this Info to myself. Im stuck at a crossroads now about being honest about my past or just letting it go and keeping it my business. I don’t want to necessarily lie or hide anything but I don’t see the point in sharing information from such a hard time in my life Or what might cause unnecessary hurt to my partner. So Reddit, AITA?