[@shylarah]
Tonsillitis would be good. Since it's caused purely by the body

Or something like an eye infection....
Wait

Pink eye or the likeness

Yes 

Do one of those....if you do go for it
Eyes or tonsales are my vote. 

Edit: 
Oh my god how did I miss that the kelpie was in the summer realm oh my goodness

*face desk*

I can edit so that someone finds our lovely kelpie