If you are playing in real time, then you won't be selling the turnips on a Monday as this is the beginning of the week and the weekly pattern, plus the prices also change at noon each day.
Most often good turnip prices appear on Wed/Thursday - sometimes the am price is the spike., sometimes a PM one.
Reading Liquefy's guide to the stalk market (in his walk thru faq on gamefaqs) or another guide should give you how the turnip market works.
You have till this coming Sat close of business to sell them, you could find someone today if they are not playing in real time or have edited their prices.