Those who are trying to live a life of faith will always find temptation from the evil one to despair and doubt. Faith, like a plant, must be cultured, nurtured and cared for. Weeds (doubt, despair) that will try and strangle it need to pulled up by the roots. Prayer, scripture, and spiritual reading are the tools for maintaining your faith and helping it to grow.
Pray the Psalms.
Psalm 130 is good :
Out of the depths have I cried unto thee, O LORD.
Lord, hear my voice: let thine ears be attentive to the voice of my supplications.
So is Psalm 42
As the hart panteth after the water brooks, so panteth my soul after thee, O God.
2My soul thirsteth for God, for the living God: when shall I come and appear before God?
3My tears have been my meat day and night, while they continually say unto me, Where is thy God?
4When I remember these things, I pour out my soul in me: for I had gone with the multitude, I went with them to the house of God, with the voice of joy and praise, with a multitude that kept holyday.
5Why art thou cast down, O my soul? and why art thou disquieted in me? hope thou in God: for I shall yet praise him for the help of his countenance.
Look into reading the book "The Way of the Pilgrim" as well. It is very good book on prayer.