What is the cause of these whispers and evil thoughts about Allah, and do they affect one's reliance and faith?

What has afflicted you is perhaps from the whispers of Satan, and you are not accountable for mere thoughts as long as you do not speak them. Your turning away from them is proof of your faith. Persist in acts of obedience, seek refuge from Satan when these thoughts come to you, turn away from thinking about them, occupy yourself with what is beneficial, beware of sitting alone, and listen frequently to the Quran.