Oh wow, after reading the description, it sounds exactly like my problem.

Thanks so much for the link! Haven't tried most of the exercises recommended here, and I'll give anything a shot at this point.

I've also never really understood when trainers say to activate, use, or strengthen your core. I do tons of advanced-level ab exercises, but my abs are never activated for my posture. My gut kinda sinks in when I slouch forward. Is it just bad habit?