What Causes Missed Periods After Stopping Metformin?

1st of my periods have been regular for the last year. Before that they were irregular. I do have pcos. Was put on metfomin. Stop taking that over 6 mo ago. My last period was dec. 16th it lasted 5 days. I've taken 2 pregnacy test both negative. How long should I wait b4 I go to the doctor