Hopefully it's the least worst option!
I know it's not really my place to say this but if it does turn out to be glandular fever/mono/Epstein Barr I'd suggest you get a second opinion on whether to use steroids during the acute phase of a viral infection (unless it's just a throat spray or inhaler or something like that).
Glad you got some sleep! I'm not a doctor and obviously they know best. I was mostly thinking about how part of the way anti-inflammatory steroids work their magic is by dampening down the immune system.