How can I make up for the fasting days I missed due to menstruation over many years, knowing that I don't know their exact number, and I find it difficult to commit to fasting?

Congratulations to the sister who asked the question for her commitment to prayer and obedience to her husband. We advise her to continue doing so seeking the pleasure of Allah. She must repent for deliberately delaying the making up of Ramadan fasts until after the following Ramadan, because that is not permissible except with a legitimate excuse. She must make up all the days she missed fasting, along with paying the expiation for delay, which is feeding one needy person for each day she delayed making up (750 grams of the staple food of the land). The expiation does not multiply with repeated delays. If she cannot determine the number of days, she must make up what clears her conscience. Consecutive making up is not required. If the delay was due to a legitimate excuse, then only making up is required, not expiation.