Join a gym. Count your blessings. Volunteer. Embrace life. Study the gospel and carry a prayer in your heart always. I'm a Big Sister volunteer and help with things around the community. I'm also very creative, I make my art and such at nighttime or naptimes, or with my kids. You can still take long walks, perhaps it's something you can involve your family in, or even rotate, one night you go alone, the next night you go as a family. It's a balancing act. Honestly, your children deserve to be your source of happiness. Sometimes, you have to stop analyzing and start living.
It sounds like though, you are trying not to use your kids for happiness... but do some sort of other activity or living the life of a child free person to fill that void. So in essence, you are still trying to put your happiness on something. Really, neither can make you happy if you aren't happy. What you do is embrace your kids. Embrace the moment. You still have a long life ahead of you and certain things can wait. You can still enjoy your life, but you also have to remember who you are. Align your goals to fit that path, but do not go out searching for activities to make you happy. The most important thing you will ever do is be a member of a family. There is a time and a season. Just like, before I had kids and got married, I like to party and go to concerts and was huge into music, I acted in plays, I also went on solo road trips.... well all of that changed when my life priorities changed. Becoming a parent is refining and selfless. I still have fun, and girls night outs, but they aren't dwelling on my mind.
Here are a few short (like 3 mins long) videos that are extremely motivational. There are about 40 of them and I watch every one when the mood strikes. They will leave you feeling motivated, and loved!
on motherhood:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
on marriage:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
you are never alone:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
tender mercies of the Lord:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
on being hopeful of good things to come:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
on creating:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
on lifting burdens:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...
on having a hard time:
http://lds.org/ldsorg/v/index.jsp?autoplay=true&index...