New medicine question.

Ma

So I went to the doctor today, he put me on metformin 500 mg for 8 weeks, the first 4 weeks will be taking 1 pill a day, then the other 4 weeks will be 1 pill twice a day. Found out I have PCOS a few months ago..has anyone taken this before? What side effects did you have? Doctor says this is the worst medicine to take, it kinda scares me..please tell me your stories!