Commiserations James. My girls gave me mumps when I was in my thirties having previously given me chickenpox which was bloody awful (off work 8 weeks, spots in every known body crevice, infected throat and frozen shoulder!!). Having mumps afterwards was a breeze compared to that!! Just a bit achey in the b***s department but quite bearable if you take something like soluble Solpadeine (paracetemol and codeine) which will also help the pains in the jaw and face. My own GP thought it was hilarious that I had got both of these complaints as an adult and said my Mum had protected me too well!!
Although there is a risk of infertility I did'nt think it was as high as your doc says. Permanent loss of fertility is rare, but up to a third of men who get this disease develop Mumps Orchitis,a consequence of which can be reduced formation of sperms (quote from a website). Keep away from any pregnant women though while you are infectious. Hope you soon feel better mate.