Haematomas will take a while to go down - the body has to absorb all the escaped blood. This can take a long time if the haemtoma is ratherlarge. There is always the chance that the haematoma is still slowly bleeding which would explain why it isn't getting smaller. Call the vet if you're worried - just a phone call will reassure you and the vet can tell you if he thinks a visit is necessary.
When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes. ~William Shakespeare