Newly diagnosed with PCOS

I have been recently diagnosed with PCOS. My doctor has done all the test and vaginal ultrasound everything looks good he says once my body is regulated. I started metformin 3 days ago today and have already started spotting and haven't had a period in months because I have always been irregular. I am hoping this is a good sign that good things are to come. Any advise or thoughts about metformin working so quickly to make me start? Thanks!!