By the way, the book that tipped me over into the Christian camp was The Reason for God, by Tim Keller.
Would highly recommend The Reason for God by Tim Keller. Super clear and to the point. Each chapter goes through a different common objection to Christianity.
I absolutely recommend Making Sense of God, and The Reason for God, by Tim Keller. Not too long ago, I was struggling with doubt so strongly that I too feared that I would become agnostic. It was this book (the Reason for God) that got me to understand that doubt was a completely normal and healthy part of the Christian experience, and that you can be both a skeptic and a Christian.
In addition, the book you'll most often have recommended to you is Mere Christianity, by C.S. Lewis , and for good reason. It's a fantastically well-written, easy to read explanation of the foundations for why Christians believe what they believe. If you haven't read it yet, please pick it up.
If you PM me with specific troubles or doubts, I can try to recommend more specific sources for those specific issues. But please, please, please start with the few books I listed. If you are serious about your search, they are absolutely essential.
The Reason for God by Tim Keller helped me a lot. It really helped me to understand that skepticism and doubt are not contradictory to Christianity.
The "problem" you seem to have is something that every Christian on earth struggles with - the disconnection between knowing something in your head and knowing it in your heart.
This is something I struggle with - there's a stark difference between being intellectually convinced of the existence of God and actually feeling like He exists.
There's a difference between knowing "Yeah, yeah, God loves me." And actually feeling the incalculable, unrestrained love of God.
There's a difference between knowing theologically that you're forgiven and actually feeling forgiven.
It's a difficult hurdle. Fortunately, God is there to help you.
God sends the Holy Spirit to us so that we can experience the presence of God, so that our knowledge of Him can drop down from our head to our heart.
For a long time, I sought an experience. I'm an extreme skeptic, so I'm always incredibly doubtful of any of the miraculous stories I hear from others. At the same time, it's because of this doubt that I so desperately wanted to experience God for myself.
I decided that, if I were to take God seriously, I would need to do whatever I could on my end to "press into" God and leave the rest up to Him. This meant that I would go to the front of the church during worship, or ask people lay hands on me and pray for me. As a skeptic and an introvert, these were huge steps for me. And many times, I wouldn't have a tangible experience with God, and I would get disheartened.
However, there have been a number of times now when I really did have experiences with God.
God lives in you. You have the Holy Spirit inside you; Christ Himself lives in you. However, for whatever reason, God sometimes gives us strong, palpable experiences and awareness of His presence, whereas most of the time we're not aware.
As someone who was originally skeptical of the "charismas," or of personal encounters with God and His Holy Spirit, I now urge you to pursue relationship with God.
That means spending time in prayer. I grew up always praying in my head with my eyes open, because I knew that God could still hear my prayers. However, I've discovered more and more that the act of going in my room, closing the door, kneeling, and praying out loud is richly rewarding. That's how people prayed throughout the Bible. I think that it helps me to connect that I'm praying the God of the universe, rather than just thinking to myself and projecting my desires.
For me, personally, walks alone and in nature have brought me closer to God. I'm someone who's always been deeply affected by nature - even in my doubt, I see the hand of the Creator in His Creation. And some of my encounters with God have been when I've been on a walk alone, not in a church.
Nonetheless, Christian community is extremely important. The Bible affirms repeatedly the importance of the church. If you're not already, try to attend church regularly and get involved with a youth group. I'm incredibly introverted, and in high school I would have thought I'd never be involved in a social group like that. However, our desire to know God should be higher than our desire for personal comfort. We need Christian friends and community surrounding us - people who will love and encourage us, people we can confide our sins and struggles to, people who will pray for us.
Worship is also incredibly important. I didn't used to sing in church. In fact, I went to a Christian school, and I would often remain seated during chapel worship. I was a Christian, but I thought that worship just "wasn't the way I connected with God." I thought that other people who are into praise music can connect with Him that way, whereas I connect with Him in other ways. While it's true that some people connect to God through certain channels more than others, we are all called to worship. I was making worship about myself - What can I get out of it? - instead of it being about God. Ironically, the more you make worship about God and not about yourself, the more you're bound to actually get out of it. This is one of the radical truths of Christianity - the more you give up of yourself, the more you truly are yourself. The more you live for others and for God, the more you're truly alive. It is more blessed to give than to receive.
Lastly, I must mention that good sermons and good books are really helpful, especially if your mind works similarly to mine. I mentioned in another comment Mere Christianity and The Reason for God - I consider them both must-reads for any Christian, but especially the one struggling with doubt. There are other good books, some specific to a particular doubt. (For instance, if your doubt has to do with the relationship between Christianity and science, then The Language of God is a must read.)
As far as sermons go, I really recommend Timothy Keller. If you have a smartphone or mp3 player, you can easily get podcasts for free.
I'll be praying for you. Feel free to PM me with any additional questions, or any particular doubts.