Yes, that's what happened for my initial periods after going on metformin. It may take a couple of periods for it to even out too, so I wouldn't be too concerned if it's not right back to normal next month either. Pretty much anytime the uterine walls haven't had the time or opportunity to fully shed the old lining, during the menses once they do shed it will be heavier, have more clots, take longer, and possibly have more cramps (they're usually caused by uterine contractions to loosen the material from the walls, so more material, more work = more cramps. Not for everyone though, or not painfully noticeable.)
Sorry I got all extra-explanatory.
I'm from a family with lots of people in medical fields, and my SO is an ultrasound tech, which means lots of OB/Gyn type stuff too. I'm also nerdy and prone to researching my medical conditions, LOL. I'll cross my fingers for you ttc in March!!