This can be a case of the half empty or half full glass syndrome depending on the glasses you are looking 
through. In your case, you are obviously looking with the half empty ones!
Restless and Unfulfilled
A good point though is that you are acknowledging that you are the one who is restless and unfulfilled – you are not blaming anyone else in your life. They appear fine with life and so have no understanding of this drive in you.
One of the causes of your pain at being unfulfilled is you feel isolated and lonely while you are going through this experience.
It is not an easy place to be as I have experienced it myself. You may also even feel that you are going mad as the rest of the world goes about its business.
The Call of your Soul
In my opinion, this is the Call of your Soul telling you it is time to stop and give yourself the space to listen to yourself, and see what you are being told. I can assure you that this inner emptiness just won’t go away until you do that – however much you may keep yourself busy. You can keep chasing your tail but it will do no good at all.
As an aside, it also makes me wonder what you are running away from instead of towards?
Coming home to Yourself
This would be a good time to see an appropriate therapist who will enable you to realise that you need to re-connect with you again and to be fulfilled from the inside out.
It will be like coming home to yourself and will enable you to be comfortable in your own shoes.
I wish you well.
Another wonderful post Irene. Yes I recognize this feeling. I spent a long time there and it still enters my life now and then. I think it probably always will as my soul is called in different directions. For me it comes back to taking personal responsibilty for my life. Loving it anyway xxx
Thanks for your lovely sharing and I know you are now taking personal responsibility – wonderful xx