You know what? I've had that happen many times. The most dramatic was when it was coming up to the date of my baptism. I was constantly plagued with thoughts questioning God's existance and my belief. I now know it the enemy attacking my belief. Even people like Martin Luther went through this. So don't think there is something wrong with you. On the contrary, something is very right. You believe enough to have cause the devil concern. He can see what a great addition you are to the kingdom of God and he wants to discourage you and freak you out and steal your joy.
So, in these cases, it's time to fight back. Knock those those lies down with the truth, God's word. Even put it in "I" terms: "I do believe, Lord. Help me overcome my unbelief. I don't need to be anxious for anything. Your word says so, so I know you are going to heal this. Help me to cast all my cares on You, Jesus, because you care for me. I am the righteousness of God in Christ Jesus, because I've put my faith in Him. This unbelief is a feeling, but it's not truth. the Holy Spirit is in me and will guide me to all truth. He who began this good work of faith in me is faithful to complete it. In Christ Jesus, I am more than an overcomer, so get behind me satan. Be gone and take your lies with you. I will never believe you."
Also, faith comes by hearing the word of God. So listen to it as much as possible. Listen to Christian music
www.klove.com and
http://www.solutionfm.com/
And to teachings:
www.lifetoday.org/beth just click that link then click on Watch Beth and choose from dozens of great teachings.
Also another great one that will help you, a great encourgaging teaching
Videos | Gateway Church
Praying for you,
A