I don't know much about PCOS/crazy periods/etc, but I work in a hospital and give Metformin to patients every day. I also ask every one of my patient's about nausea, BM's, etc. and have never in my 7 years of doing this had someone say anything that seemed to link these problems to metformin (this could be because they had previously tried metformin and was taken off and put on a different med before I met them). Anyways, all this to say that if your MD does prescribe Metformin, don't be afraid to atleast try it. I've seen a lot of posts of side effects people have from that medication on this site, but I just want you to know that although some people do have those problems, a lot of people don't. You never know how your own body is going to respond. Maybe it will be something that works wonderful for you, if not, atleast you'll know you tried.
P.S. It's a pretty common medication and I'm guessing most MD's won't have a problem prescribing it
Good luck! I hope you find something that works for you!