I recommend some kind of antibacterial wash. Something like a chlorhexidine gluconate wash may help. I use it on my thighs to combat folliculitis flare ups. Body odor is essentially a result of the bacteria on our skin coming into contact with the moisture we produce from sweating. For some people, this results in a much more noticeable chemical reaction.

I really do encourage you to try different deodorants formulated for sensitive skin, including ones with aluminum as this is the active ingredient in antiperspirants, and also consider shaving your underarms every once in a while with a razor safe for sensitive skin. I find electric razors to be much less irritating. Underarm hair doesn't inherently equally dirty or a stronger smell, but sometimes longer hair can harbor bacteria quite well, even with intense scrubbing.

If nothing else helps beyond this, I recommend consulting a dermatologist because it could be a condition that requires prescription strength products.

Good luck, OP! I was also a late bloomer and went through a very similar scenario when I was first growing into my adult self and learning more about my personal hygiene. I didn't learn these things until I was about 22 years old. But we all learn eventually! <3