Very few people can make me cum just by felatio, so you are not alone. When someone does manage, I tell them they are part of a very select group. I've learned to be satisfied even if I don't come, but sometimes my partners are very upset if they don't get their "reward" for all their effort, or they get the wrong idea, and think they are not satisfying me.
It's important to me that my partner should be satisfied, too, and if I sense they really want a load, I find some way to give it. Usually, I'll do someting else (kiss, etc) for a couple of minutes while I use may hand to bring myself to almost the point of no return, and then let them give me head again, and I will cum if I time it right. I'm sure it's not as satisfying to them as if they had done the whole thing orally, but if done tactfully and smoothly, everyone ends up happy.
Sometimes I can also make myself cum during felatio by becomming agressive, rather than passively receiving head. In other words, by giving someone a good face-fucking rather than letting them suck me. Of course, while that does turn some people on, more often than not it's not what they like. You might also experiment with things like breath mints, etc, which can cause heightened or diferent sensations. This may be enough to get you off.