Now, you've tackled and issue of mine. Hmm I don't think that happiness and fulfillment are the same but they do go hand in hand with each other.
I had a very long period when I had some family problems and had to make a break from school, stay at home and look out for a family member, and I can't even bring myself to describe properly how miserably and unhappy I felt for not being able to do what I like, or to do anything besides obvious care-giving. Work is something that gives you an opportunity to challenge yourself on a daily basis, to show your strength, to have something of your own. You'll have a family of your own someday I presume and although you'll love them with all your heart you'll need some place and something that you do by yourself and for the most part for yourself (this is if you get the money part from the equation and don't consider the reasons of supporting your family). That is what I consider fulfillment and happiness for the most part.
In my line of work I think that creative process is the most fulfilling and the part of the work day that I have to spend outside my office, at the place where all the equipment is installed, working and actual processes are. You get to see how brilliant is the human mind for thinking of such an amazing things, for making them work, for finding new ways to build something, control something, improve something.
The part of my work involves maintaining the measurement and control devices in a district heating boiler rooms. Now, when you get in that room, which is not really a room, more of a large warehouse, you get to see a huge boiler, lots of pipes, measuring equipment, valves, mechanical devices, motors, pumps and such. People evolved from heating water above the open fire to using coal chambers for heating and having someone administering coal in them, to doing all that by automatic control, and having only a handful of people around to monitor it all time. I find that amazing, that amazement is fulfilling and fulfillment makes me happy. I've got no idea if this makes any sense to you.
What is fulfillment for you? Where do you seek and hopefully find it?