A few years ago I also dropped a big can on my big toe and was in agony and I honestly thought I had broken it (and didnt think anything could be done about it) so didnt seek medical treatment straight away. 2 days later it was still very sore so I went to the medical centre at work and the paramedic said it was the build up of blood under the nail that was causing the pain. He drilled it and got all the blood out and it was instant relief so if the nail is black it might be worth getting it looked at incase they do need to drill it.