could be irritated ulnar nerve some things you could try is sleep with towel wrapped around you elbow at night to keep it straight. also dont lean on your elbow when driving or just sitting it is a very common habit we all do and it can damage the nerve. hope this helps.
have you found anyhing out yet . cause i'm the some way except it's in both hands but also both hands go numb too.i'm 26yr female mine will happen through out the day walking,driving,sleeping, playing w/ kids,cooking i'm getting very tired of this .i'm still going to look for help if i find any will chat back to you i'm twinzoo on here