Measuring Small !!

I went to my Ob/Gyn and was told my baby is measuring @33+2days. I am 36+4days and I was so surprised because I eat so much I don't know why he so small. He said my baby is 5pounds and 2ounces most likely be 6pounds +ounces when I deliver. He told me he is going to weight about the same as my first child 6pounds and 4ounces. This really have me thinking but the ultra sound never always be right.