Doubts are common among Christians and should be handled with truth and grace. Tim Keller offers good advice for Christians and their doubts.
The only way to doubt Christianity rightly and fairly is to discern the alternate belief under each of your doubts and then to ask yourself what reasons you have for believing it. How do you know your belief is true? It would be inconsistent to require more justification for Christian belief than you do for your own, but this is frequently what happens. In fairness you must doubt your doubts. My thesis is that if you come to recognize the beliefs on which your doubts about Christianity are based, and if you seek as much proof for those beliefs as you seek from Christians for theirs–you will discover that your doubts are not as solid as they first appeared.
Timothy Keller, Reason for God, page xxv