Anterior Pelvic Tilt explains my pop-out belly when relaxed?

I love FitnessBlender workouts and programs! I'm a strong, fit, healthy-eating, okay-sleeping 40yo woman. No one would look at me and say I am anything other than slim and fit. However, I feel like I am always having to hold in my stomach. This issue is not a new one, I would say my whole life I have felt like my midsection was "too big", I've never had a flat stomach. When I let it relax, it's like I am months pregnant or something. Recently, in a quick Google search, I came across some discussions on "anterior pelvic tilt" (APT). Has anyone heard about APT? Do you have a similar issue? If so, were you able to resolve it? Or, is this normal? Do some people have flatter and/or rounder stomachs than others?