I had mumps (for the 2nd time) at 27 years old... felt fine, came to work, and was promptly sent home by the horrified men on my floor! Had a cushy two weeks off... (actually studied hard for my theory driving test and got that sorted!). But yes, I was told at the time, that you can have it a second time IF you don't get a full blown version when young. (and how would we know if we'd had a full blown version or not?!)...
Or might you have an abscess in a tooth? I've had that too!! aaah!
Been there, got the tshirts! Hope you're ok!!