Hi Jarrod, I think that your problem steems from your masturbating, Now as guys if we are not careful we can apply a little bit more pressure when we do it, ok so far, now if thats what you do, then theres your answer and it comes from this quote, what is done by the hand, is remembered by the brain, so when having oral sex your g/f does not apply the pressure that you are used to, I think in that case you should just use oral as a foreplay, but you could get your g/f to finger you anus while having oral, I bet that would work, its all down to her massarging your prostate and bingo, that should get you off.
Good Luck
(And frankly, there is no reason they should be, if they aren't.)
Try moving to vaginal sex before orgasm, if she's on the Pill. Some guys just aren't comfortable ejaculating into a person's mouth.
Try your g spot the anus. but if your not into that have her play with your testicles