I'm pleased to say that the antibiotic has calmed things down wonderfully and it looks like the doctor was right. It isn't a sinus problem after all. Now the stabbing pains in my upper jaw and the ache up near my ear have abated, the real problem is now emerging. It seems to be a tooth.
In the lower jaw.
How this can cause the pain it did where it did I haven't a clue, but I have now located a tooth that seems tender when I bite experimentally on something like a toothbrush handle. It's a tooth that was re-filled a few weeks ago during my last visit to the dentist.
Tomorrow I need to make a dentist's appointment. :(