I am a girl who get yellowish discharge now and then even in prayers. Is my wudu valid ?

This discharge breaks Wudhu. If it is so serious and continuous that it carries on for an entire salaah time, without you getting a chance to perform the fard salah, then you could be classified as a mazoor (Excused), however if that is not the case then it will be necessary for you to make wudhu after the discharge and remove all impurities from your body.

This discharge is impure, thus any pads worn to stop the flow would have to be removed if the discharge is more than a dirham. (Fatawa Mahmoodiyyah Vol.16 Pg.160)

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai