I have no idea why I am losing with nocturne.
I hate to be one of "those guys" who blames their team, but it seems uncanny that literally every game I play with Nocturne, either my team feeds and no matter how hard I try to carry, it is impossible to carry the team after every enemy carry is fed pre-6, or someone AFKs.
A few sample games:
Unwinnable super feeding bot lane dies multiple times pre-6: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2063781029/213933916?tab=overview
Top laner AFK for 10 minutes: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2063781029/213933916?tab=overview
"support lux" first buys Doran's Ring and intent feeds because she didn't get mid: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2063154440/213933916?tab=overview
Another one where my team gives up FB and allows enemy team to snowball: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2062981354/213933916?tab=overview
Another solo death bot. http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2062960640/213933916?tab=overview
or 
is a good defensive item on him.