Are you already in a vocation and feel fulfilled, or like me still trying to discern? Sometimes I find myself asking God if He can just print out a "road map for life" that would be as simple as google maps. Then I realize google maps gets you lost, reroutes you, and tells you your destination is a burned down school--yes that actually happened to my uncle. We are not going to get lost in our discernment if we are seeking God's will. He desires to show us the way more than we want to follow it!
I have known people who have tried vocations in so many ways. One person was engaged to be married, then realized she had a vocation to religious life. Another was in religious life in one convent, tried a second, and ended up perpetually professed in a third. One was one year away from ordination and then realized he did not have a call to the priesthood, eventually met his wife.....and their son became a priest! None of this is infidelity to what we first tried, but rather a generous openness to wherever God leads! His ways are not our ways.
An ultimate failsafe for a vocation is peace. You won't be flooded with unshakeable doubts if you are on the right road. Uncertainty is normal in any big decision, but there will always be a calm, quiet conviction deep down that rests in your heart. Having that in our vocation is crucial because it will require perseverance until death and will be the means of our sanctification and the sanctification of those around us.
It is always important to have a spiritual guide in discernment because they can look at our life objectively, when we often feel clouded by our own feelings. Friends and family can often point out to us what is obvious that we cannot even see. Good books can tell us even more. We don't have to feel like our life is a question mark. Even when we finally discover our vocation, there will be things we don't have answers for throughout life. I think God allows this so we always rely on Him--always turn to prayer. We don't have it all figured out--no one does but God.
If you're trying to figure out what God wants for your life, I can relate. It's difficult and you're not alone. That's why we have prayer to remember each other before God in seeking to become saints. Have courage. Sometimes when we feel we have so many questions, maybe what we need to ask ourselves is, are we really listening to what God is telling us?