Metformin PCOS & Periods

Meg
Day #3 on Metformin: 
Doctor Prescibed me Metformin, due to absent period for over a month, (LMP 17 April 2017) 
was diagnosed with PCOS in 2015, and I'm not ovulating (progesterone tested before metformin) 
My dr told me it should bring on my period, but I should give it atleast 2 months to work. 
Day3: my vagina feels heavy like it's going to fall out/slight cramping like my period is coming on. 
I was wondering how long it took for metformin to give you your period and would it be too early for it to kick a period in?