Baby's belly measuring small??

I just had my 29 week growth scan. The doctor said baby's weight is normal (2 lbs 11  ounces), heartbeat normal, head and bones measuring normal, etc. However, his belly is measuring small. His belly has been measuring about 10 days behind for a couple months now, but they always said no big deal. I guess now they're concerned and said he's not getting enough protein. They told me to eat a high protein snack every 2 hours (?!) and come back in 2 weeks for another scan to remeasure his belly. Has anyone else been told this?