Bella - I could have written that myself, almost word for word. I think Asherman has it right. Though it's hard to tell "thinkers" not to think. It's what we think we do best.
I also think Cav has had an impact this week in my thinking even more along these lines. He was so young, and here I am at 42 having not accomplished near as much, or embraced life nearly as well as he did.
As for purpose, I had a rather trying period several years ago with way too much thinking taking place. In the end I came to the quiet conclusion that our purpose is to be happy. Not just "be happy" but all that it entails, such as loving ones self, accepting that others have their own journey and being okay with it, letting things roll off rather than stick, taking pleasure in little things, and do the things you want to do that add to your happiness.
For those of a religious bent, which I had more of at the time than I do today, I came to this conclusion with the understanding that us being happy IS what makes God happy and honors Him. Just as we delight in hearing our own children laugh, and play and enjoy life, isn't it possible God also delights in seeing this in us, since God is our father? What greater honor is there for a parent than to see our children happy? Loving life? Playing gleefully, even in puddles? Being pleased with an accomplishment? Learning new things? And, believing in God is not required to understand this simple concept.
You are certainly not alone in your feelings. So, how about this... Let's each make our own private list of things we want to accomplish, experience, learn and do over th next year. Each week we have to choose one thing from the list and take steps towards accomplishing it.
Some will take more time than others causing overlap. I may want to join Habitat for Humanity, and I can't be done with helping to build a house in a week. But this week I can join HFH, and next week I can plant bulbs after I finish my HFH commitment for the day. And the next week, I can move on to #3 on my list and get the kids photo albums up to date. And, after that I might sign up for a cooking class.
So, not all of the things have to be world changing or long term. Just things that will bring you a sense of happiness and accomplishment. By looking at your list you'll see that you are accomplishing things as you mark them off, and you'll have directions for where you want to go.
Wanna give it a try?