ER or wait it out?

It's 5am and I have been experiencing extreme uterine cramping that woke me up half an hour ago, so bad I've had to take a painkiller and it's giving me the sweats. Thing is, I'm not on my period. I'm about a week and a few days out until I'm supposed to get it. I have Endometriosis so it could be just that, or from a terrible and similar pain I had four years ago, it could be a miscarriage (and all they did that time was give me painkillers). Should I wait?