Metformin

So we have started seeing a fertility specialist and getting our test done. My period just started today (after 45days!) and I will be getting my hsg procedure next week. But my dr called today and she said she wants to put me on metformin because my a1c is 6.3 and glucose is 134. She told me to take it at night with dinner. I am reading about horrible side effects (mainly diarrhea). I already have a nervous colon and I can’t imagine what this pill will do to me. Any advice? Experience?