Doubts are always pulling me down. Slowing me in growing closer to God, and playing with my mind. Fighting them off takes a lot of strength as I try and find the right answer. Sometimes my doubts are useful, to make me think twice. Like when I was thinking of buying another guitar. My doubts said "Do I really need one? Will I ever use it?", and in the end stopped me from making a rash decision.
When it is your core beliefs, doubts become a bit more complicated. Because, what you believe deep inside you will affect how you think about everything. So how you do survive when you are struggling in doubt? Believe.
Believe that you are in God's hands, believe that he will take care of you even in this patch of darkness, and believe God's love that smothers any doubts you might have. Remember the times you were joyful, the times you looked at God as your solid rock, and remember that as a rock, the foundation of God will never turn into sand.
Believing even in doubt might be a paradox, but it is a sure way of getting through those doubting phases. Hope for the day that you can look back at those patches and say "How stupid I was to doubt God back then".