Does inserting a finger to clean discharge invalidate the fast, and what is the way to clean it for someone who suffers from its abundance without needing to repeat ablution?

Vaginal discharge is pure, and one does not need to perform istinja' (ritual cleansing) from it. If it is continuous, then one must perform ablution for each prayer. It is permissible to adopt the view of the Maliki school, which states that continuous minor ritual impurity does not invalidate ablution if it causes hardship. It is not permissible to insert a finger into the interior of the vagina, as this resembles sodomy and tribadism, and it is an act of innovators (mubtadi'ah). It has no effect on the validity of the fast, and these whisperings (waswas) should be ignored.