3 days ago i smashed my finger. it has turned black under the nail, it is numb and leaking a clear fluid from under the nail. should i be concerned?

Pressure: Black in finger is blood. Probably been trying to get out, that's why it's leaking, physicians usually make a small opening or help to release the pressure, so you can start the healing process faster. I would personally recommend seeing a physician to see if you would benefit from such a release of pressure. Usually sooner the better. There might be no treatment if none is needed.

See dr.: You may have so much swelling and fluid that your nerves are being affected causing numbness, and you may need the pressure under your nail relieved. always best to get the area evaluated and assessed so treatment can be started to help.

Possibly: You have what's called a hematoma under the fingernail. A Hematoma is basically a collection of blood that's trapped between the skin and the under surface of the nailbed. Due to the buildup of blood there is pressure on the surrounding tissues, including the nerves and this can result in the numbness. Clear fluid is OK.....cloudy fluid could be a sign of infection (a reason to see your MD)