For an average strength fragrance like Bleu de Chanel for example, I will do 1 spray on the chest, 1 on each pulse point on my arms, and 1 on each side of my neck for a total of 5 sprays. You can spray your shirt or hair for a little extra. Obviously stronger stuff like 1 Million or Joop! will need less sprays. Just make sure you spray on exposed skin.
I spray the first shot on my chest thanks to a tip from Marc aka Robes08 aka The Fragrance Guru. The first spray from a bottle might not be a full spray so it's good to "waste" it on your chest while also giving you a little more sillage from body heat. I used to spray on my inner wrists but now I spray where my arms bend b/c it's a larger area and I won't accidentally wash off my fragrance when washing my hands.
There's a good chance you just have olfactory fatigue and can't smell your own fragrance after the first couple hours. That's good. It means your brain is functioning normally. It tunes out constant smells that it deems non threatening so you can pay attention to anything new or alarming instead.