Black spot under toenail?

all right so ive had this black spot on my toenail next to my big toe (2nd toe)... its black with little red dots behind it it looks like blood... ive been reading and im worried it may be a fungus... but it is slowly moving upwards as my nail grows, so im wondering if when it reaches the top, if i should cut it? i cant remember if i maybe stubbed my toe.... my hsoes are all fine, so no problem there.... i dont where open toed shoes, but i walk barefoot in my house (we all do)...