Poets used to have styles, but now that we're offspring of Romantics and Confessionalists, uniqueness of voice is what matters - modern readers seem to want to know the person behind the words. Eavan Boland considers it more essential than ever that poets should discover "a real voice, a true voice". Of course, this authentic voice may not turn out to be distinctive, but unless it is, no-one (not even the writer) will be any the wiser. Paz in 'The Other Voice' thought that "the singularity of modern poetry does not come from the ideas or attitudes of a poet, it comes from his voice", and Harold Bloom has noted that "When we open a first volume of verse these days, we listen to hear a distinctive voice, if we can, and if the voice is not already somewhat differentiated from its precursors and its fellows, then we tend to stop listening, no matter what the voice is attempting to say."
But do established poets really have a voice? Maybe if you pick a particular phase of their work (as with Rich), or just their best pieces (as with Larkin) they may speak with one voice, displaying a distinctive mood, language, vocabulary and form, but over a lifetime there's usually quite a diversity. Besides, for some newer kinds of poetry the concept of being true to one's inner voice isn't appropriate. I think there's a case for saying that when writing we adopt a poetic persona, and like an actor, we gradually feel ourselves into the part. Some of us are character actors, happy to explore different styles, others stick with what gave us our breakthrough role. But having a distinctive voice doesn't ensure quality; it could be affectation.
So if you're told you have a voice, don't jump for joy. Maybe you've just become rather set in your ways. It makes good business sense, but if it means that your poems resemble each other too much, then there's a danger of self-parody. Even at workshops there's detrimental typecasting - people are likely to greet a new poem with "it's not like your usual stuff" rather than judge it on its merits. Especially if you're young you may want to challenge the authority of this voice before it takes you over. Take a rest from writing, lock away your old poems and notebooks, seek out new influences, try dramatic monologues. You may even consider submitting poems under different names. If nothing else, these activities will add nuances and new inflections, helping you to lose your voice - with style.