What is the ruling on fasting the first and third days, and what is the ruling on breaking the fast on the second day, after seeing drops of blood at the beginning of Ramadan and its continuation with a yellowish discharge, knowing that the blood was not abundant?

The three days during which the questioner saw blood are days of menstruation. It is impermissible for a woman to fast during her menstruation, and she must make up those days after Ramadan. Her fasting on the first and third days is invalid due to the absence of a condition for the validity of fasting, which is the cessation of menstrual blood.