I've used a thermometer that doesn't actually beep. I had to watch the thing until the little tiny "F" stopped flashing. That said, for my 19 month old, I've always prefered to take his temperature rectally. I lay him on the changing table on his side, facing me, then I insert the thermometer in (after covering the tip in vaseline), and he just lays there. He hates when I hold him tight to take his temp. under the arm, and so do I b/c all he does is cry and fight it. You do need to make sure it's the right kind of thermometer, though. The one I have is just for rectal temps.
I've used the temporal thermometer, and maybe it's just user error, but I HATE those thermometers!! They have one at the daycare I used to work at, and it rarely read the same temp. twice. On one kid, 5 min. apart, it would read 96.7 and 103.0. It wasn't just me who had problems with it. I know it's fast, but I personally don't think it's accurate. I hope your baby feels better soon!