Metformin w/ PCOS

So I started taking Metformin a little over a week ago for my PCOS , I had a miscarriage a few months ago & we have been TTC ever since. It took us almost 4 years before getting our BFP last time. I was suppose to start my period Monday but ive still not had any spotting or bleeding at all. I have been very crampy as if I'll start any minute for days now. Could the metformin be the cause of my late period or can I maybe have some hope for a rainbow baby ?