What is the ruling on fasting and making up the days I missed or fasted while experiencing dark, foul-smelling bleeding a week after performing ghusl following menstruation, especially given that the bleeding was caused by irregular use of birth control pills and coincided with travel? And is this considered deliberate breaking of the fast?

It is not permissible for a Muslim woman to be lenient in learning the rulings of menstruation and istihadah (definition) (post-menstrual bleeding), and she must ask the people of knowledge. If this returning blood can be considered menstruation—that is, if it appeared within the fifteen-day period (the maximum duration of menstruation according to the majority of scholars), meaning that its total days, along with the days of purity and the days of menstruation preceding it, amounted to fifteen days—then it is menstruation, even if it does not repeat three times according to the Shafi'i school, in contrast to the Hanbali school, which stipulated its repetition three times. However, if the period exceeds fifteen days, then it is istihadah blood.