I think its gotta be mental, but may be physical.....i can get off in like 1 or 2 minutes if I masturbate, but with sex.....im in for the long haul.
Kid, you answered your own question.
Don't touch yer own dick for about two weeks except to exercise and watch how it reacts to yer Ol' Lady's pussy.
What you've done is train your nervous system to only respond quickly to your own hand.
Y'gotta re-train it for a woman.
In short: Never again masturbate.