Just found out I have GD

This is my 3rd pregnancy, but first time being diagnosed with GD. I'm 27w+5d and they are concerned with the babies size, mostly his abdomen. It's measuring at the size of a 32 week gestation baby. Today is my first day monitoring myself and changing what I eat. I'm actually feeling really awful, I'm feeling weak and dizzy. I'm following exactly how my MFM Dr wants me to eat and how often, but I feel worse than ever. Is this normal when adjusting at first?