When I was in my twenties, I went through three different major crises of faith. Most of them had to do with never really considered some aspects of Christianity.
The answers were out there but I simply did not know where to look.
I also had no idea other people were dealing with the same issues. Below are extremely helpful videos if you have ever had doubts about what you believe and why.
Dr. Gary Habermas is the foremost theologian on the Resurrection. He is also extremely good at philosophy and working through doubt.