Wa'alaikum asalaam warahmatullah,
Doubts or waswaasah (whispers) are very common among all Muslims, we all get them on different levels - some have them bad and don't know how to tackle them other people are able to deal with them and keep them at bay. Heres a section of a helpful fatwa, I have only extracted what I think you need to read. The question asked was regarding doubts/whispers. And may Allah make your situation easier for you, ameen.
"If the Shaytaan manages to instill some doubts in a person’s heart concerning Allaah and so on, he should not worry about that, because he is only suffering these doubts because of the faith in his heart. The person who is not a believer does not care whether he doubts or not; the one who suffers because of these doubts and whispers is a believer. The Prophet (peace and blessings of Allaah be upon him) said, “That is clear faith,” (narrated by Muslim, no. 132) , meaning that what the Shaytaan casts into your hearts of such matters is a reflection of clear faith, i.e., sincere faith… He described it as sincere faith, because the one who experiences these doubts is not happy about them and should not pay any attention to them; they grieve him and he does not want them. The Shaytaan only comes to hearts which are filled with faith in order to destroy it; he does not come to hearts that are devoid of faith, because they are already ruined. It was said to Ibn ‘Abbaas or Ibn Mas’ood that the Jews said, “We do not experience waswaas during our prayers.” He said, “Of course, what would the Shaytaan do with a heart that is already ruined?!”
My advice to her is to ignore all of these whispers. She will find it hard at first, and she will think that she is praying without wudoo’ or without saying “Allaahu akbar” at the beginning, and so on, but it will become easier for her after that, and this doubt and waswaas will leave her, in sha Allaah.
Praise be to Allaah, there are people who suffered with this problem, but they were told how to deal with it and how to resist it, and Allaah granted them relief. We ask Allaah to keep us safe and sound.
Kitaab Liqaa’aat al-Baab al-Maftooh by Shaykh Muhammad ibn Saalih al-‘Uthaymeen, p. 14"