Does the doubt about me being menstruating—given the presence of the yellowish discharge and the usual pre-menstrual fatigue—affect the intention to fast the days in which no blood was discharged?

Yellowish or brownish discharges are not considered menstruation unless they occur during the habitual period or are connected to blood. Hesitation in the intention to break the fast does not invalidate it; rather, it is the firm resolve to break it that does. Therefore, doubt about menstruation does not affect the validity of your fast as long as you have not consumed anything that breaks the fast. Your fast is valid, and you are not required to make up for any days except those you explicitly broke due to menstruation.