Most of the time, I have no trouble labeling myself as a photographer, but it seems the hesitance tends to seep in when other photographers stand nearby with bulky gear and enormous telephoto lenses, muttering technical terms or using white balance cards. It seeps in to laugh at me while I'm on Flickr looking through other photographers' portfolios, or when I'm about to enter a photography contest and I change my mind after browsing through the entries gallery. A few times, it's gotten to me so much that I'd actually tried to change my style or binge-learn new techniques. Then I'd get frustrated with myself, and I'd put down my camera for a while. I'd only pick it back up when I had enough time to sort through my own photos, without the opportunity to compare my work to the work of anyone else, and gain some self confidence back.
Comparison defeats the purpose of passion. Your passion is uniquely yours, and nobody feels it the same way as you. Be proud of your pace instead of trying to catch up with everybody else, or you'll destroy something special. Not knowing every little detail about your favorite thing in the world doesn't make your passion any less valid. There's always going to be somebody out there who knows more than you do, and there's also always somebody who knows less--but who cares anyway? Don't feel threatened. If you've got nothing knowledgeable to say, tell people how fast your heart beats when you're doing that thing it is that you love, and talk for about it for hours. Let your eyes light up, let them see how much emotion you use to fuel your passion. They might even be jealous, because maybe they don't have as strong a passion as you do.
Call yourself what you are--an artist, a scientist, a photographer. You don't need anything but passion to earn that title.