Salaam,
I feel relaxed, at peace, and happy, and extremely close to God, but it is not like this sometimes. I don't doubt the book. From what I have read so far of the book, it just can't be possible to be written by a human. I doubt the existence of God few times. It is not all the times, but there are few days like this or few times, but then I find such thoughts very illogical. However whenever I get such thoughts, my love for God increases more than I ever had before.

Basically whenever I feel uneasy, I reject those thoughts and when I feel at peace, I go towards that. It is like this with me since childhood. When I feel uneasy in my heart in doing something but I still do it, I always end up being wrong and regret it. When i feel right for something and go for it, it always end up being good. So my heart I feel at peace and happy in believing in God, so I can not reject such feelings. It is not just feelings though. There are other reasons too.
In the end, I just to pray to God to give me the guidance and put all my trust on him, those uneasy feelings and thoughts stop.
May God always guides me.