An unbeliever should not wait, expecting that somehow God will let him know without a doubt that he exists and is calling him, for that moment will never come for almost all of us (I have in mind exceptions such as the call of St. Paul by Jesus). Faith is required. If you cannot possibly dismiss Jesus completely from you heart, the time is ripe for accepting him. Once you take the leap of faith, your doubts and uncertainties will diminish over time. They will totally vanish when you attain union with the Lord. Faith is absolutely the key.