When we ask, "What should I do with my life?" the implication is there is one and only one answer. Is that really the case? I think there's a better question:
"What do I already enjoy doing and would like to do more of, given the opportunity?"
Thinking about what you already like to do or feel you are good at gives you a legitimate starting point. You might find your purpose already exists but simply needs some fine tuning. Focusing on what we "should" be doing starts us down a path of guilt and obligation, rather than inspiration.
I believe purpose in life is ever changing, never static. It evolves as you do and as the world changes. This dynamic approach to purpose is liberating. It allows your skills, likes and desires to morph into the next phase of your life as your situation changes.
Some of these changes will be brought on yourself, as when you move to a new job, get married, etc. Some of these changes will be more subtle and gradual, as when you realize you are good with a camera or seem to have a real gift at teaching Sunday School.
Finding one's purpose helps to keep life fresh and new. It's valuable in a number of ways. But it should never be used to hammer you over the head with guilt or regret. If you don't feel you have a purpose right now, give yourself some time to reflect. Start with what your already enjoy doing.