Is the yellow discharge that occurred between 11/11 and 19/11 considered menstruation, must the missed prayers be made up, and is the fast of 23/11 valid?

If the bleeding period exceeds fifteen days without an interruption of purity lasting thirteen days, then you are experiencing istiḥāḍah (non-menstrual vaginal bleeding). In this case, refer to your previous menstrual habit, and consider anything beyond it as istiḥāḍah. If you do not have a habit, then act based on differentiation: what you can distinguish as having the characteristics of menstrual blood, observe that period, and anything beyond it is istiḥāḍah. If you have neither a habit nor differentiation, then, based on estimation, observe six or seven days as menstruation, and anything beyond that is istiḥāḍah. As for the prayers you missed, thinking you were menstruating, there is a difference of opinion regarding the obligation to make them up. Your fasting on days of purity is valid.