Smile vs life

Just saw a pic if me when I was 17/18 - big giant grin and an obvious happiness that is almost palpable. It's extraordinary looking at pics up to that age and seeing it over and over again (ok except when I was 13 and hated everything. Ah teenagers!). It used to define me, that smile, it was a guarantee, people described me by it - always smiling, such a happy person to be around... and it was true. 

When did I stop smiling, when did the worries take over? I was always an introvert, so it's not the social side of things, but there is this constant worry, this burden of responsibility, this desperate need for planning and for things to go right (aka according to plan) that wasn't there before. And it seems it's here to stay, stronger, darker by the day. It feels like I move between worrying, being anxious and depressed and being organised, planning and cooing... but the smile isn't there in either... occasionally yes, and it's real and Shows happiness but it's fleeting and carries no weight. 

When did it all change and why?