What Causes Pain And Swelling In Penis After Circumcision?

My 2 1/2 y/o son had a circumcision today with release of some adhesions. He is awake crying with pain. His penis is extremely swollen and unable to see the penis head at all due to swelling. I know some swelling is expected, however this seems to be too much swelling. We are considering taking him to an ER. What is your recommendation? We are giving his pain med as ordered. Thanks.