Metformin

Anyone in metformin for being insulin resistant? My levels are really high and low vitamin D. So they want to start me in metformin im kinda scared to take it. Idk why. I ovulate everything month but my progesterone and everything is to low to conceive. The dr said I could lose 40 pounds and change my diet that it could help. That would put me at 130 pounds. What do you guys think? Is metformin worth it? Are the side effects really that bad? And how long did it take you to conceive?