My baby's belly is distended?

My one month old baby boy has a distended belly. It is distended right below his belly button. It is hard and sticks out more when he cries. It seems to cause him pain when I try to rub it or touch it. He has not pooped in over 40 hours. He was up all night last night crying, this may seem normal for a baby but he has never stayed up all night and usually sleeps great. He also wouldn't eat from midnight to 8 this morning because he was crying so much. He is eating now and has calmed down after I gave him baby tylenol. It is sunday today so I am going to take him to the doctor tomorrow but I was just wondering if anybody else had experience with this.