You're probably thinking of a man whose son had been taken over by an evil spirit. One day, he brought his son to Jesus and asked Him to heal him if He could. Jesus replied that all things were possible if we believe, and "Immediately the boy's father exclaimed, 'I do believe; help me overcome my unbelief!'" (Mark 9:24). His exclamation was actually a prayer for help and Jesus responded to his prayer by healing his son.
The most important thing I can tell you is that God wants you to have a strong faith. He doesn't want us to be spiritually weak and wavering! And because He wants our faith to be strong, He has given us everything we need to make our faith grow. Just as we need food to grow strong physically, so we need spiritual "food" to grow strong spiritually.
What is that spiritual "food"? First, God has given us His Word, the Bible. The man with the sick son listened to Jesus' words and his faith grew stronger as a result. Make the Bible part of your life every day.
Then God also has given us the privilege of prayer. This man cried out to Jesus and Jesus answered. Bring your concerns to God every day, and learn to trust them into His loving hands. Finally, God has given us other believers to encourage and help us. Ask Him to lead you to a church where this can happen. Make use of God's spiritual "food," and your faith will grow strong.