How can I find the reasons to create my purpose in life?

Hello AL, thank you for submitting this question! I hope I am able to give a helpful answer.

It sounds like you are doing fairly well in life overall, at least relating to some of the more primal needs such as a stable living situation and income. It sounds like you are seeking fulfillment on a higher level, which is commendable. You indicate that your value system includes being able to make a difference in the lives of others, or perhaps the world, which sounds like you care a lot about the value categories of personal relationships as well as community. This might be something to lean into. A great many folks hyper-focus on areas of their lives which bring financial success or other forms of structural stability, but ignore their own more existential values - and who can blame anybody, when this is a direct result of the way our society is set up, for better or for worse. There is a type of therapy called Behavioral Activation, which comes from the school of Cognitive Behavioral Therapy, which is exactly designed to focus on helping people feel better by exploring areas of life which have been under-nourished, and helping develop a plan to explore those areas of life to seek fulfillment in a step-by-step manner. If you are able to find a therapist who specializes in Cognitive Behavioral Therapy, and specifically Behavioral Activation, this may help you greatly, but also there are many articles and worksheets about this practice which are available by way of your favorite search engine.

The idea of exploring new challenges can sound overwhelming, but it does not have to be, if you break this down into very small, manageable and attainable steps. You will not necessarily change someone else's life or make an impact on the world on day one, and that is not the goal. The goal is to start by perhaps making a list of possible ventures which meet your values of relationships and community. Then narrow that list down into options that seem the most appealing, and develop a step-by-step plan to start addressing those goals. Count every step you take as an accomplishment, even the first steps of looking into these goals. In fact, even writing this question on here counts as an accomplishment, as far as I am concerned! 

You sound like an intelligent person, and you may be interested in stoicism and/or existential philosophy. Victor Frankl and Albert Camus come to mind. Having said that, I really do not think that anything beats the human experience of one-to-one therapy, as reading is great but having a human being to bounce ideas off of, help you process, and work through difficult situations with you is an immensely helpful process, to which many can attest. 

I hope this has been helpful, and I hope this is a first of many steps for you seeking greater fulfillment in life, and gaining more full control over your moods and sense of self. I wish you the best!