If you spray and sniff your wrist constantly, your nose will gradually "deaden" to the scent and you'll have to really cram your skin up to your nose to get anything. And if you wear a fragrance more than, say, three or four days in a row, the lasting power and projection won't be as evident. I once went on an Opium binge where it was the only thing I wore for about two weeks, and I remember being slightly let down by its rather minimal projection by the end of the second week. Took a break from it for about a month, then decided on a whim to wear it again. Holy F-balls, I was still getting wafts of its sillage a good 9 hours after spraying (and this was the eau de toilette).
Olfactory fatigue isn't just a buzz phrase on the fragrance forums, it's real, and all too common. If you want the full effects of all your fragrances, you need to rotate them and take breaks as needed. Also, wear the damn things, don't spray your arms and compulsively sniff them all day. I get a much better impression of a scent's sillage and projection (hey, that rhymes) when I just spray it on my neck or chest and go about my day.
Of course, once you've eliminated those variables, you could just have sinus problems or whacky skin chemistry. Do ask for a second opinion when you find you can't smell the fragrance anymore - chances are you're projecting just fine (especially with Joop!).