I'm sorry that you feel like this @PointlessMother
Apologies for the bullet points but a few things came to mind as I read your post...
*Do you think some form of grief counselling might be helpful for you?
*Have you worked out your why yet? If not, have a read of Simon Sinek's book.
*Arthur C Brooks book called Strength to Strength which might resonate with you and give you some comfort at this middle stage of life.
*Another book recommendation - Quiet by Susan Cain, it might help you to see the benefits of being an introvert, rather than the negatives that society seems to want us to believe about ourselves.
*I hope this doesn't sound insensitive, but when able, consider reading the 5 Regrets of the Dying. It might give some insight into the things that people find valuable & purposeful in life.
*Again, I hope this does not come across as insensitive but if you were to be diagnosed with a life limiting illness now, how would you live out your remaining time? What would be important to you, what do you have an urge to achieve and get done?
- If you were forced to sum up your life's achievements so far and you had to use a "strength based approach" or shine a light on the positive things you've done, what would be on that list? A PhD is a huge achievement and it is a very committed piece of work. What is making you feel like it isn't and why are you playing down it's value? Has someone else played it down and then made you doubt the value of it and yourself?
*Would you consider volunteering with the homeless population or people with multiple disadvantages or similar? It can be a really humbling experience that makes us appreciate all that we have.
I hope things become clearer for you OP and I hope that you find something that sparks your interest. Good luck.