You thought you were an atheist? that doesn't even make sense, you either have belief or not. Rejecting God or ignoring Him is quite different than fundamentally questioning the reality of it. Most likely you rejected christianity for about 4 months but the concept of God was still quite real so after certain experiences or guilt you came back to God.
On the contrary, it makes a lot of sense. St. Mark 9, 24: And straightway the father of the child cried out, and said with tears,
Lord, I believe; help thou mine unbelief.
This is the paradoxal situation of a christian, we believe, hence we pray, and yet we ask God to forgive our unbelief and to increase our faith.
