Need to lose 70 lbs

I need help! I need to lose 70lbs or so to make myself eligible for <a href="">IVF</a> in case we need it. Right now, I weigh 270 and have a BMI of 40. I have PCOS with insulin resistance and it seems like I just can't lose weight. I'm obviously not doing something right. I am taking Metformin extended release 500mg three times a day, but so far it hasn't lowered my insulin level yet and I haven't lost any weight. 
I'll take any advice that helped you!