How soon should I get my period after starting metformin?

I am 20 and haven't had a period since January. I actually never have periods unless I take birth control or provera. My doctor believes I have PCOS based on acne and absence of period. I am not trying to get pregnant. She started me off at 500 mg and I will be going back to her in about 2 months.|||The metformin is to help with insulin resistance known in P.C.O.S. Once your blood glucose levels have gotten better things may start clearing up for you and I found in myself anyways about a month after I was on metformin I got my period back about a month after being on it (was still very irregular for about a year but now almost on a 30 day track). If you are able to keep tabs on your glucose (a blood meter) and watch your diet (try a gluten free one) you will almost be sure you will find major improvements.|||Isn't metformin a diabetes medicine?|||I've heard it generally takes about two weeks. Though I could be wrong.