It could have derived from 2 things:
La concha de tu madre! = Your mothers cunt!
Concha es tu madre! = Your mother is a cunt!
Either way is a pretty good insult!
Literally translates as "Your mother's sea shell".
Colloquially as translates as "Your mother's vagina".
One hundred percent translates as "motherfucker".
"You've shot me in the kidney, ¡concha tu madre!".