Baby too small/not growing

I am 28 weeks along and my doctors say the baby weighs a little over 2 pounds. They claim that he should be nearly 3. I'm no doctor but all the online charts say he should be 2.22oz. They want to give me steriods to get his lungs mature and have basically promised he will be a preemie. I'm having a c-section, no surprise there due to my other 2 c-sections previously. I have diabetes type 2 and hyperthyroidism. The diabetes is not well controlled but I have been working hard to get my sugar lower. They can't seem to tell my why my baby isn't growing and it scares me a lot especially because they say his heart is healthy, he is moving a lot, . I have been diabetic for nearly 6 years so I'm not a stranger to the condition. Is anyone else here having anything remotely similar to my situation, or have been before or can offer any info or support?