Here's your issue. If I am not just reading too much into this, you're ACTING humble. in other words you're being phony.
Upon first impression that might seem genuine, but if it is indeed just an act, then people pick up on that shit, whether they're aware of it or not. One cannot "act" humbly without genuinely being humble.
Just because you think you're "acting" humbly, doesn't mean that's how you're being perceived by anyone else. And you dating timeline suggests the girls, once the initial period of infatuation wears off and they begin to piece together a proper assessment of your personality, consciously or subconsciously, notice that it's an act.
I mean, look at it this way, I don't doubt you're a bad looking dude, but all of the evidence you've given us suggests there are flaws with your personality that is being picked up on. Reassess yourself, your goals and what you value in yourself and others.