Late period with Metformin?! Common?

Ok ya'll need a little advice - I've been taking metformin since I wanna say maybe october - I had a chemical pregnancy in April so my periods were screwed up for a while...well since taking metformin I've had what seemed to be like regular periods the first few ones were spotty but all were 27-28 days was like clockwork. Well, today is cycle day 29 and I don't even have an inkling of a sign that my period is coming. I took a pregnancy test last night (cycle day 28) and it was it normal to have a late period on metformin?! I'm just so discouraged right now šŸ˜” I really thought my periods were back on track!!