Does metformin and vitamins delay period?

Hi ladies, i would like to know if any of you has had this happen. I was put on metformin 500 mg on june 13 and got my af on june 21st on cycle day 34(which was good comparing to having longer cycles), i also lost 11 lbs since then but did not get AF for the month of july, i am now on cd 42 and no AF so far and did many pregnancy test and they all came out negative. I also take vitamin b12 1000 mg and folic acid 400 mg. i was told that metformin regulates the period how came i am late? Please help :(