Why is my nose ALWAYS congested?

Ok, so I am a guitarist and singer. I can play guitar fine, but my singing is bothering me. I like my singing, but the one thing holding me back from completely liking the sound of my voice, is my nose. It's very hard to explain, so I hope I can manage to explain it well enough. Basically, even when I can breathe just fine through my nose, it still always feels as if it is stuffed up deep in the back. I have cleaned out my nose many times, by blowing it, and using cotton swabs. Every day I make sure that it is completely clean, but it never helps, because deep back in my nose, it always feels as though I am congested. For example, I can breathe through it with no problems, but if I try and sniff very hard, I can feel how completely stuffed up it is. Honestly, I think this is the reason my voice has been so nasally-sounding ever since I was a little kid. (Sorry for making the question so long.)