Hi, My Baby Seemed To Be Constipated A Couple Of

Hi, my baby seemed to be constipated a couple of days ago, pushing, getting distressed, having tiny solid dropping like poo... Then yesterday he has had around 5 dirty nappies all very dark green/black and seems uncomfortable within himself. His bottom does not look sore but he is very upset and uncomfortable.
Should I be concerned, does he need to see a doctor?