It's not you, it's Facebook: Messenger is down in many parts of the world
At this very moment, it looks like Messenger is down for most users on the East Coast of the US and in Europe, as well as for folks in Canada.
Facebook has yet to comment on the matter, but it certainly seems that the company is dealing with some serious issues right now. Meanwhile, the Facebook website itself and the Facebook mobile app seem to be working fine - but that doesn't really help if you want to send messages, or see older conversations.
If you want to, you can check out a Facebook Messenger outage map at this link. Let us know if this outage is affecting you, okay?