How much methylone have you been using? How often? I recently did 4 days in a row of high-dose with multiple redoses with 4-EMC (another serotonin releaser). The past 2 days before this one I felt like I was the walking dead, could barely get sentences out, I felt very weird and depersonalized. It's been a few days and I feel pretty good today. You just gotta slow your roll man. But yeah, methylone and other serotonin releasers definitely make it hard for me to get it up, always have. Doesn't seem to happen to some people but it does to others.
If you could tell us more of your experiences/situation we might be able to provide better advice. In general, it's not good to abuse these things. You need to keep them to special, infrequent uses. As much as I understand how hard that can be (particularly regarding empathogens like methylone).