Natalie,
Since you can't pinpoint an obvious insult to your hearing, your case sounds similar to other people who've had their central auditory gain suddenly increase (for unknown reasons), which greatly amplifies head sounds, like tinnitus.
The tinnitus you're hearing now may have been there already, but you couldn't hear it--until your brain cranked up the volume and made you sensitive. So now, with the volume of your brain on high, you're suddenly hearing everything louder--the movies, the crowd in the restaurant, grocery freezers, your tinnitus--all things that were there before, but that you never really noticed. It's just one of the variations of hyperacusis that some people get.
Hypothetically, if your brain turns up its perceived volume by ten decibels, your formerly quiet head will suddenly expose all kinds of head noises, and a garbage truck will sound like the end of the world.
As bad as it sounds, I hope that's the case for you, because if your brain eventually turns down its volume on the world, it may well turn down the volume of the tinnitus along with it.
I can't speak about the possibility of your work headset as a contributor (but I wouldn't doubt it). However, if you had just been to a rock concert, or had taken a poisonous drug, it would be cause for concern. But the cases like yours--in which the hyperacusis comes from nowhere, for no apparent reason--seem most likely to resolve over time. I sincerely hope you are one of the lucky ones.
In any event, if it goes away for you, be sure to avoid loud noise and heavy medications--forever. Your experience may be a warning that you are susceptible.