I think everyone has doubts, but sometimes they can be overwhelming, so I'm sorry if you're feeling that level of doubt. I myself spent some time as an Atheist because my doubts were so overwhelming, and it was a terrible dark time in my life. I wish I had a magic cure for you, but honestly one single thing didn't pull me out of it. Talking with many people, being open to truth, and reading a lot is what helped me in that extreme-doubt time.
One thing someone said to me once (though it doesn't help a ton DURING the doubt) is that it's actually great when you experience such things, because it means you're leaving behind the smallness of what you once thought you knew about God (or what someone else told you) and now it's time to have a personal relationship with Him that you'd never get any other way. He is so much bigger and grander than the tiny box we sometimes put Him in, and doubt is a way to break the walls of that box! I see the truth in that now, but again, it doesn't really help the heartache that comes with doubt WHILE you're going through it.
Just remember He is bigger than your doubts. Truth always rises to the top, so never fear seeking truth. If God is truly God, He will be there waiting for you (and I've found that's exactly the case!).