I have heard many people express their doubts. Usually it takes the form of, "I don't know, sometimes I feel God is real but if he is wouldn't [fill in the blank] happen (or not)?" And then the thought is dropped. If you have a doubt or a question about God's existance don't build it on feelings, although they can be a confirmation the existance of God can be based on facts. Also, if you have a doubt or question then explore it. Look for the answer. Don't just leave it for another day.
    Today I was reading in John 7 about the crowds who were witnessing Jesus speak. A lot were saying, he has to be the Messiah - would the Messiah perform as many miracles as this man does? And then some doubted asking, "How can the Messiah come from Galilee? Does not Scripture say that the Messiah will come from David’s descendants and from Bethlehem, the town where David lived?" (John 7:41-42) Then it says the people were divided as a result. Wait a minute, that was their doubt and why they didn't believe? But, all of us know that Jesus was born in Bethlehem so he was from that town although he didn't live there. They could have just asked Jesus this! Jesus would have known what they were saying, he could have clarified it! Further on the Pharisees are discussing arresting Jesus and one of them stands up to suggest that they should at least investigate the man before pronouncing him guilty. But they bully him and use the same logic that worked on the crowds by saying, "Are you from Galilee, too? Look into it, and you will find that a prophet does not come out of Galilee." (John 7:52). And then they went home. He should have looked into it, found indeed that a prophet does not come from Galilee but find out where Jesus really did come from. So, don't let anyone or yourself bully you out of looking for the answers yourself. If you ever have any doubts, look into it!