Do my feelings of remorse for sins and my desire not to return to them count as true repentance, given the presence of whispers and doubts about the sincerity of my repentance?

Praise be to Allah who has accepted your repentance. Have a good opinion of your Lord, and know that He is more merciful to His servant than a mother is to her child. Strive to fulfill the conditions of repentance and righteous deeds, for indeed, good deeds efface evil ones. Leave aside your obsessive thoughts and do not give in to them. We hope that your repentance is sincere, so you must strive to rectify your actions, do many good deeds, and continue to abandon sins.