What Causes Swelling Under The Penis Head After Circumcision?

my son was circumsized 12 days ago he penis has been healing okay however when his bandage fell off we noticed that he had swelling under the head of his penis its like. he did bleed a lot after the circumsicison. will this go away a friend told me that it might be hematoma since he bled. my son says the bulge is not painful. he does not have high temp so it might not be an infection. help!