When I grow up

I would like to have a job that makes me happy and fulfilled. I have this bad habit of being content with what I am doing at a particular moment as opposed to being content period. I used to think I knew what I wanted to be when I grew up, but to be sincere, after getting a degree in what I thought I wanted to do, I am in another field entirely and okay with it, but not necessarily happy or fulfilled. I don't know that I've ever had a job that made me really happy and that bothers me. I am young and have about 40 more years of work ahead of me and I am scared that if I do not find the job of my dreams soon, I will be stuck in a cycle of discontent and have to settle for a job just because it pays the bills.