ANSWER:
This is natural as iman of a believer goes up and down.
What you must keep in mind is that you must never leave a single obligatory worship and keep yourself away from sins as much as possible and keep your mouth moist with the remembrance of Allah all the time and maintain your daily adkar without fail and keep good company with practicing brothers all the time so that they they will only encourage you to do what’s good, this will boost your iman and keep you away from sinning by the will of Allah.