Hello,
Trauma to the nail can cause blackening of the nail because of injury to the nail bed and spillage of blood in nailbed.It does not sound like a fungal infection.This bleeding can resolve on its own and if the symptoms of severe pain persists then drilling of the nail to release the blood may have to be done.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional queries.Kind regards.
Injury to nail due to trauma it self can cause the features described.With out a fungus test,woods lamp done, not safe to give internal antifungals.