Purpose: what is it, where does it come from? I am skeptical that there is any one ultimate "purpose" which is the sole source of feelings of meaning and significance in our lives. It seems to me that there is a plurality of factors - friends and family, love, personal projects, beauty, knowledge, sports, etc. - that contribute to the flourishing of a human life which we might very well not be able to ground in some ultimate purpose in a way that is not trivial.
Now given that we recognize this plurality of values, there are a couple of things one might ask. First, one might inquire what is the source of our association of values with these experiences or activities and I think this question is one that might be most aptly answered by some evolutionary account. Further phenomenological analyses might also bring light to what it is exactly that we value about different experiences.
Secondly, someone who is currently feeling down and unable to find value in their own life might hope for an answer or medicine for their plight. These people I would first and foremost refer to psychotherapists and other experts who might best be able to diagnose their particular problems and help them solve their own problems. It is also possible that these people might find solace in some life philosophy, such as stoicism or existentialism, but I find it equally likely that the key to their lock might be found in a number of different activies like painting, running or reconnecting with nature.
Thirdly, one might ask the properly philosophical questions "But what really makes for a meaningful life?" or "How should we live?". The answers to these questions might identify ways to live that differ in significant ways from the previous list of experiences and activities that we find valuable. For example, an extreme utilitarian might possibly think it appropriate to devalue their families and commit their lives to producing "the greatest amount of happiness for the greatest amount of people". Nevertheless, I personally find that the most convincing answers to these questions are ones that, in addition to perhaps offering some ethical imperatives, recognize what we already find valuable and offer us ways to better manage these sources of value, as I find the case to be with Aristotle's works on ethics.