Coming up on 40 and not happy

I am coming up on 40 and I feel like my life is a complete bust. I left the workforce to take care of my son and have not gone back because I feel like I have spent to much time out of it and it would be starting all over. My marriage is best described as ok- there isn’t much lust but there is love. My life is dominated by the activities both my husband and child have but not myself. I need to change something because I can’t imagine living the rest of my years is this mild unhappiness. Has anyone found happiness and change of life after 40?