T2, pregnancy & insulin.

I'm a t2 diabetic which I control with metformin and diet. When I'm pregnant I need insulin. Right now my biggest issue is my fasting number. I take Humulin at night for my fasting blood sugar, since I'm pregnant they have even tighter ranges for where my numbers need to be. My endo wants my fasting number 5.3 or under. This is starting to feel impossible. With my 1st child, I had absolutely no issue with my fasting number. My weight is now lower than when I was pregnant with her, yet I'm on 3x the amount of insulin at night to lower my fasting number and still nothing. Right now I'm getting readings of 6.3-6.6. All my endo does is keep upping my insulin and it doesn't seem to bring my numbers down - without insulin they're around 6.6 - 6.8. I'm rotating my injection site, I've tried various places too (buttock, thigh and upper arm). I have a low carb dinner and snack before bed and it still doesn't help. I have no idea if I'm doing something wrong. Has anyone got any advice? I feel like it's probably something trivial.