Does Metformin Helps To Regularise Periods?

Hi,I have PCOS since 18 years old. Have been on Yasmin for many years.Now I am 31. Since I want to have a baby,doc put me on metformin and clomid. For the first time last month I had my first real period on the 23rd of June.(For the previous time had to take medicine to induce it) but this month which is my 3rd cycle of clomid,I have not had my period. Will metformin make period regular one month and absent the other month?