Are my fasting and prayers valid, knowing that my period is irregular and stopped after taking period-delaying pills, then returned, and I continued to fast and pray?

The blood discharged by a woman is considered menses as long as it does not exceed fifteen days; otherwise, it is considered istihadah (non-menstrual vaginal bleeding) according to the majority of scholars. If your bleeding exceeds fifteen days, the excess is istihadah. You should perform ghusl (ritual purification bath) and observe your customary period, which is seven days—if your last period before the istihadah was seven days. If your customary period is in the middle of the month, you observe it starting from the middle of the month.

The blood discharged on the second day of Ramadan is not menses because it occurs in the middle of the month, not at its beginning. The minimum duration of purity between two menstrual cycles is thirteen days, and this blood was not separated from the previous menses by 13 days.

If the bleeding does not exceed fifteen days, you are not considered to have istihadah, and your fasting and prayers are valid.