I journal, writing about past experiences and wonder in writing about possible interests.
What has helped me most in figuring out myself is to read self-help books about issues, such as anger, that I know I need to look at. I got started doing this the first time I went to counseling. I was around 30, wanted to be married and have children but felt that wasn't going to happen. She gave me a book to read about being co-dependent. At first reading it made me angry. A year or more later, after reading other related books, I realized that I was co-dependent and had to focus on finding ways to make myself happy without depending on other people.
I have always had at least one friend with whom I could talk about interests, hers and mine.
If finding things to do is part of your goal, I suggest that you try out different activities. Take the 4yo to the library for story time where you'll meet other mothers who may be in a similar quandry but who also have other activities/interests that you can learn about.
I now view life as a continuing process of learning about myself, my world, and growing as I make new discoveries. With this philosophy I still have a purpose when I feel brought down by negative experiences. It's gotten easier over the years for me to bounce back from the negative.