Hmmm... I seriously think you should be testing your pills before dumping 'em in your throat... sounds to me like you're getting bunk pills.
Yeah sure... I do believe that tolerance most definately plays a role in alot of cases where the effects aren't felt, but... by the sounds of it, you haven't been dumping riduculous amounts of MDMA in such short spaces of time, or you haven't been doing them for all that long. Besides, I hear that those dependant on MDMA still do have the ability to roll, it's just that their actual "roll" has been lowered significantly.
But... you have got to realise that "chasing" that first peak you had from your first time is probably one of the worst things you could do. Many people's effects of MDMA/E have been reduced since the first time they took their pill (Much like me with Meth/Speed.)
That's not to say, "You're never going to feel the effects of "e" again." But... maybe after those first couple of times... your body is probably trying to tell you that the "Novelty" of dropping bikkies is wearing off.
Only thing I can reccomend is maybe not even thinking about having a night out on the pills, EVER! Try and forget about your good nights out on them (yeah right!! Easier said than done!) and just let it slide for a bit. Then maybe later on down the track, try taking one or two... and if no luck?? I'd say give up!! and move onto something else.
That's one really good, good thing about pot. After the first time (for me anyways...) it works just about every single time.
Goodluck mate!