I have had mass shedding of the baby hairs when they reach the end of their lifespan. I assume it was the hairs that went away at the same time. When I was your age, still presenting male, I was losing hair but unaware of that loss. It didn't become obvious until I was 26. So mpb can happen unnoticed for a time. I hope for your sake that the shedding you noticed is just your hair getting ready to be longer, thicker, full and permanent!