What Causes Diarrhea And Pain In The Lower Stomach?

Hi, I have been told to have PCOS for the past 10 years atleast now. I'm trying to get pregnant so my doctor has me on metformin 500mg, 1 pill 3 times a day, but I am only able to take 1 pill for the past 3 weeks. I have been sick in te 3 weeks of taking the pill, headachs every day, diarrhea, pain in my lower somtach, sometimes feels like it's my ovaries, like I will start my period. Something else I have noticed, is my breats have gotton bigger also. I took a test at home and came up negative. What could be causing this?