Insulin levels rising again?

My insulin levels were coming down on metformin but on this round of bloodwork (4 months since the previous), it's back up to being high, higher than it was originally. How does that happen? Is the metformin not working anymore? Is there any other next steps or other meds to address this? I'm seeing my endocrinologist in 2 weeks and now I'm really nervous what she is going to say