I don't know why you're so skeptical that a drug possessing the primary effect of flooding one's brain with serotonin can cause SSRI withdrawal symptoms upon cessation.

As for whether or not it's 'really MDMA', not everybody is popping pressed ecstasy tablets. It's trivial to send a few crushed crystals to a spectroscopy lab and I very rarely see samples cut with anything other than carbohydrates.