What should you do about missed prayers if you cannot differentiate between the yellowish discharge and the white discharge after menstruation, and you do not know exactly when the white discharge appeared?

If a woman doubts during her period of purity, she should add the doubted time to the nearest time when it is likely to have occurred, because the original state is that menstruation continues until purity is confirmed. Whatever she doubts, whether it is menstruation or purity, the original state is that it is menstruation. She is not obligated to make up prayers except for those she is certain she missed after purity was attained. It appears that the questioner is experiencing waswas (obsessive whispering). She can act upon the opinion of those who do not consider yellowish discharge to be menstruation at all, which is the choice of Sheikh al-Islam Ibn Taymiyyah, if that is easier for her.