I also have PCOS and was infertile until my doctor prescribed Metformin for me. We'd tried for nearly 6 years. I took it for about a month or so and became pregnant. It was prescribed to me to take one pill a day for a week, then 2 pills a day for a week, and then finally 3 pills a day for a week. This builds some tolerance in your system and keeps the side effects at bay. I took it again when I was breastfeeding because I was literally CRAVING sugar and couldn't get enough of it and when I did my research found that the Metformin helped take care of that too, and it did. I'm a little lazy with taking pills and went off them again when I weaned my daughter and then starting taking them again when we decided to try conceiving again.
Each of the three times I started them, I had a sudden bowel movement about 3 hours after taking the first pill. After that, I really didn't have any side effects. So, now wanting to start them again so that I can hopefully get pregnant, I will start my first pill on a day that I don't have to worry about where I am when it hits me.
I look at Metformin as my miracle pill to getting pregnant and don't mind the side effects. It also saved me from gaining another 20 pounds while I breastfed.
It will also help you curb your sweet tooth even if you aren't breastfeeding. It is helping your body use the insulin correctly.
Good luck. Just give it a try over a weekend you don't really have any plans. It really isn't that bad (or at least it wasn't for me).