Why does the sound of my voice vary so much throughout the day?

by Dane
(Las Vegas NV USA)

I don't understand it. Most of the time my voice sounds like I'm short of breath, and feels tight sometimes. Because of that, all of the things I say in a friendly or jokingly matter comes off very wrong and ends up offending people, thus ending me up in isolation.

However, once in a blue moon, my voice can sound wildly different, and come off very smooth and relaxed, which the same people I've spoken to (of whom I referred to above) give me a much better reaction, and are more accepting towards me. But, it doesn't last long... After a couple hours, that "relaxed" sounding voice is gone. And then I'm back to the other voice, where I'm unable to execute proper tone and delivery..

After so many years of negative reactions I've received in due to the way I sound and being completely misunderstood because of it, I finally realize what the problem is. But I don't know how to fix it.. What do I have to do to keep my voice sounding smooth, or, the way I believe its suppose to sound?