I once had a really bad headache for over a year after an operation as a kid. No pain killer has ever worked on me (over than general anaesthetic obviously but when I woke up I was in pain), despite trying different things.
Once I had glass in my ear, and they put the stuff to numb it on, but that didn't work, so the nurse just carried on stitching up my ear with no pain killer!
I don't bother with pain killers anymore if I get ill, as I might as well save my money cos I know it's not going to work!