To say that you have no purpose in life is just a thought, an activity of the mind. The next minute or day you will say, I know exactly what I want to do, which is also a thought. The activity of the mind is a complex web of endlessly shifting memories, images, moods, and ideas. To be confused with your direction in life is a symptom of taking your thoughts seriously. But how can you take them seriously when one minute they say one thing, and the next minute something else?
If you must have a purpose, why not make it to find your original nature, your essential being? What else could be more important? To become rich and famous? Riches and fame are fleeting. All achievements are fleeting.
If you must have a purpose, find out who you really are. Are you really a collection of short-lived thoughts, memories, moods, and sensations that experiences the world from a bag of perishable skin and bones? Or are you the unalterable aware presence that knows all of the comings and goings of the temporary body-mind and ever-changing world yet doesn’t come and go with them?
Your choice: rest in the eternal peace and understanding of your unborn being or suffer and die at the hands of an illusionary self.