didn't ejaculate while having sex!!!!

- hmmm, so here's the thing, me and my gal were enjoying one another and we end up in bed, good for me and her...lol

we end up having sex and i'm goin' at it as i've done many times before without any problems, and this one time, here i am giving it my all and with the condom on (as always and yes, i always do cum inside it while having sex) this one time giving it my all, condom on and such, i'm all up for it so to speak and nothing comes out!!! i tried missionary style, legs on the shoulders, dog, spooning and such, and hmm...time has passed, i'm exhausted by now and not a thing out of me...i tell ya, i was spent and noooo clue why noooo cum...i was so tired, i had to give up...and now, this has happened twice, tell ya, it's not making me feel any better now??...sad huh???? (girlfriend even asked the tell all question "is it me"??? i said, nooo, guess my 'lil guy took the day off again...lol

any clue as to why this happened or so?? was it just a one or two time deal??? should i be worried?? 'cause i tell ya...i sure feel frustrated when it happends, twice now!!!

concerned? :-(