I'm going through terrible situation of my faith , I don't know how to protect it , doubts appear in my heart about Allah swt , that literally depresses me , my heart aches , I just can't bear these doubts ,

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Know, dear questioner, that a Muslim may have some whispers that he thinks to be doubts, but in reality, it is not so. Rather, within his own self, he is a believer. The sign of his faith is his hatred of those thoughts and his fear and aversion to them, and this is clear from your question, dear brother, that you hate them, are afraid of their consequences, and your heart aches because of them. This is evidence of your faith, Allah willing.

Abu Hurayrah reported, that some people from amongst the Companions of the Prophet came to him and said, “Verily we perceive in our minds what everyone of us considers too grave to express.” He said, “Do you really perceive it?” They said: “Yes.” Upon this, he remarked, “That is the manifest faith.” [Muslim]

An-Nawawi said:

“Manifest faith and pure faith mean that considering it too grave to express is the manifest faith. Considering it too grave to express and their intense fear of it and of uttering it, let alone believing in it, then this is from someone who has really achieved complete faith and has no doubts ... It means that the devil whispers to the one whom he is unable to lead astray, so he makes his life hard by whispering to him because of his inability to lead him astray. As for the disbeliever, the devil comes to him from wherever he wants, and he does not only whisper to him, but he manipulates him however he wants. So, this is the meaning of the Hadith, the cause of whispers (waswasah) is pure faith, or waswasah is a sign of pure faith.” [End of quote]

What we recommend you to do first is to refrain from those whispers altogether, as repelling them is one of the best means of getting rid of them. Secondly, we recommend you to recite the Quran as much as possible while pondering over its meaning, as it is a cure for all diseases of the hearts such as whispers, worries and doubts.

Also, strive to profusely supplicate Allah to make faith firm in your heart and to beautify it for you and make you love it, repel doubts and whispers about it, as Allah disposes of hearts the way he wishes.

The supplication that the Prophet said most frequently was: “O Changer of the hearts make my heart steadfast in Your Religion.” [At-Tirmithi]

He also frequently supplicated: “O Allah, Turner of the hearts, turn our hearts to Your Obedience.” [Muslim]

Also, pondering over the creatures of Allah, increases and strengthens faith. In the Book of Allah, there is an invitation to those who doubt to meditate on His Creatures, as in Surah Ibrahim (what means): {Their messengers said, "Can there be doubt about Allah, Creator of the heavens and earth?} [Quran 14:10]

Tahir ibn Ashour said in at-Tahreer wat-Tanweer:

“The name of Allah was followed with the description that indicates His Existence, which is the existence of the heavens and the earth, which indicates that they have a wise Creator because of the impossibility of the existence of these wonderful and organized creatures without a Creator Who chose to create them. This is known with the least ponderation.” [End of quote]

For more benefit on whispers about Allah, Kufr and creed, and how to repel them, please refer to Fatawa 396772, 389311, 85823, 356689, 174507 and 18353.

Allah knows best.