Baby too small

Hi ladies..went to the doctor today and found out I lost 5 pounds...currently 28 weeks...they say my baby boy is measuring wayy behind ...they say I need to drink more water and eat every two hours..even though I eat constantly...seems I'm not doing anything right with baby #2 ugh..so disgusted with myself..any advice?? ..I need him big ..like yesterday..July will be here before I know it..