I have had this problem a couple times over the years, and a past doctor thought I had Sjogren's at one point. Sometimes I have some borderline symptoms, but no official diagnosis. Prednisone cleared it up once, and antibiotics the second time. I was extremely ill and incapacitated for about a week each time. The first time, they thought it might be mono, too.
Anyway, I haven't had another flare up of this since I was officially diagnosed with Lupus (Lupus headed south to my kidneys and has focused its efforts there). Your paratitis sounds way worse than mine, but I did want you to know that you are not alone.
Good luck in finding the source of this and a treatment that works. I'll be thinking of you.