Planning meals

Maybe I should just preplan meals ahead of time for at least one week at a time.  I tried to plan daily but my diet is poor and it is not working.  I have not lost any weight and with having Polycystic Ovarian Syndrome, it would make weight loss even harder.  I know that I need to change but I don't know how.  I am now thinking about cooking food the night before and making a plan for the day since I make daily plans anyways.  That way, I won't have the common problems I have been having.