Metformin

I was prescribed metformin in hopes to conceive. Prior to starting my period was non existent for about a whole year. 2 months into metformin my period came . 2months in a row for a full 7 days now the third month its no where to be found. Which should be good if I was pregnant but my test ate negative 😭 has this ever happened to anyone? Metformin get your period going and then just stop it ???? Please any feedback would be greatly appreciated Thank youuu☺️