^^ good advice.
MDMA all but shuts down your immune system anyway so if you're already sick then at best you'll still be just as sick the next day, but more than likely you'll feel worse. Not to mention if you're going to an event you're probably going to get everyone around you sick too.
That said, tomorrow night is NYE and I know that even if I woke up sick tomorrow morning I'd still probably carry out my plans...been looking forward to it for too long now, lol. So if you must go, don't share any water or anything with anyone, take some vitamin C (no cold meds!) and be prepared to feel twice as bad the next day.
As far as taking meds goes, as far as I know taking a normal dose of ibuprofen to help control your fever isn't going to interact badly with MDMA, someone please correct me if I'm wrong. I do know that many cold meds contain DXM though and that is something you definitely don't want to mix.