I'm not PCOS, but I do take Provera every 3 months to (try to) have a cycle. I was taking it every month for about 6 months, and my experience was that for the ten days I was taking it each month, I wouldn't lose anything, then a day or two after I quit taking it, I would start losing again. Maybe coincidental, but I never thought so. (Thanks for the reminder, I'm supposed to take it again in November.)
I would advise you to ask your doctor when to take it. My doctor had me take a ten day cycle once a month.