These doubts and evil wiswaas are from Shaytaan. There are some duas which you can say in order to get the shaytan away:
first seek refuge from shaytan (Aotho Bilahi minashaytanirajim) Allah the Most High said, “And if there comes to you from Satan an evil suggestion, then seek refuge in Allah. Indeed, He is the Hearing, the Knowing.” [41:36]
Recitation of soorah al-Baqarah. The Messenger, sallallahu `alayhi wa sallam, said, “The house in which al-Baqarah is recited is not approached by Shaytan.” [Muslim]
Reciting Quran in general aswell as Shaytan runs from recitation.
When whispering during the prayer:
“O Messenger of Allah (SAW) verily Shaitan comes between me and my prayer and recitation making me confused The Messenger of Allah (SAW) replied, that is a shaitan called Khanzab so if you sense his presence then seek refuge in Allah from him and spittle on your left three times. He said, I said that and Allah took him away from me.” [Saheed Muslim (14/189-190)]
(Im not sure if u can say this during prayer or u shld say it before, maybe sum1 else can clarify :/)
I hope this helps!
Remember brother NEVER lose hope in Allah SWT and this wiswas is also a sign of imam because the Shaytan only comes to people who a righteous to misguide them, he doesnt need to wiswas with the disbelievers as they are already on the wrong path :)