Is the fast considered valid if a small amount of yellowish discharge appears after confirming purification from menstruation and taking pills to avoid a long make-up period?

It is permissible for a woman to take medication to stop menstruation if it does not result in harm, and she is considered pure when the bleeding stops. As for yellowish discharge, if it occurs during the accustomed period or is continuous with blood, then it is considered menses. Consequently, fasting on the days it occurred is invalid and must be made up. If it is not menses, then your fast is valid.