Is what I feel – this lack of success in performing acts of obedience and their scarcity after my repentance from a sin I committed – a relapse or a punishment, and what should I do?

The ill effects of sins may deprive a servant of some acts of obedience, harden the heart, and stand between him and the causes of mercy. Al-Hasan al-Basri said: "Your sins have shackled you." Ibn al-Qayyim said: "Among the effects of sins is deprivation from obedience." Therefore, increase in repentance and seeking forgiveness, and remain between fear and hope regarding the acceptance of repentance.