SUPER confused

Ok so I've been on MetFormin for a month now, give or take. I haven't had a period since February and I thought taking it I would start my cycle immediately. But I started just 4 days ago. Is it doing what it's suppose to be doing? How do I know? I've always been irregular so I would be expecting it soon anyways since I have a cycle every 3-4 months or so. I just want a BFP so badly and it's killing me it's taking so long and so much =[