Helping Newborn with Constipation?

My son was born on March 18th. He has been extremely healthy and happy up until this point. But, he hasn't pooped in two days. So, today he was very fussy. Every time he tooted he was extra fussy. It looks like he's trying to go.. but nothing comes out. How can I help him? Should I call his pediatrician? Is this normal for newborns to expereince?