What is the ruling on fasting the vow on Mondays and Thursdays after a lapse due to health problems and childbirth?

"Making vows (nadhr) is not legislated, as the Prophet, peace and blessings be upon him, forbade it. However, whoever vows an act of obedience to Allah must fulfill it. So, if you are able to fast what you vowed, then you are obliged to fulfill it. If you are unable, then you must offer an expiation for breaking an oath, which is feeding ten poor people, or clothing them, or freeing a slave."