I have been having disgusting thoughts about Islam and Allah. It makes me sad and I want to cry. I don't enjoy having the thoughts. Some of these thoughts are shirk and other disgusting things.
Question: By thinking shirk, have I committed shirk?
I'm very scared that I may have fallen out of the fold of Islam, and be in hell fire forever.
Verse (49:14) The bedouins say, "We have believed." Say, "You have not [yet] believed; but say [instead], 'We have submitted,' for faith has not yet entered your hearts. And if you obey Allah and His Messenger, He will not deprive you from your deeds of anything. Indeed, Allah is Forgiving and Merciful."
Read this ayah 2 3 times to understand the main point.
I have been gone through this situation until I learned Arabic Grammar and read Quran again and again, now I have full faith in Allah.
Spend some time to make your IMAN firm and strong.
As for as I know, if you are not deliberately thinking about it then it is not shirk. If these thoughts come to your mind not by your "will" then also it is not shirk. Shirk "is the sin of practicing idolatry or polytheism" or at least believing that there are more than one God.
I suggest you to just memorize surah Al-Ikhlas. It is said that "Whoever understands it and believes in its teaching, will get rid of shirk (polytheism) completely". See https://quran.com/112
Believe comes after doubt. If you never thought "is there a God?" how would you believe there is a God? If the thoughts that came to you are so horrible(not questions for belief but questions with no aim like who created god) you are supposed to ask God to make the devil go away from you, try praying to him(verbally or a full prayer) and try not to think about this stuff again.
