Great question. Given that you are only 20 years old and these voices have been around "for years," I am skeptical of a schizophrenia diagnosis (i.e., they may not be traditional hallucinations). Based upon your written description, it is more likely that you developed a sort of self-talk to help you cope with some of the really bad times. It is a grown-up version of how lonely kids will create an imaginary friend to help soothe or comfort them when they are bored, anxious, worried, etc.
In fact, some of the recent theories of auditory hallucinations in schizophrenics is that the "voices" they are hearing are actually their own inner-thoughts. In other words, they cannot distinguish their own thoughts from the world around them. Taking this notion a step further, I am thinking that your voices may in fact be related to trauma, and were originally developed to help you deal with trauma (which would also absolutely drive an agitated depression, BTW).
As far as treatment goes, it sounds as if your friends think you MAY have a problem ,but you do not think so(?). If the counseling and meditation have helped, then I think you should return to them. Also try yoga or some sort of guided imagery exercises to settle your thoughts. Based upon the info you supplied, it does not sound like medication would be necessary, although a thorough evaluation by a qualified professional should be conducted if this problem seems to grow worse, or if it hovers beyond your ability to cope. If you are satisfied with the response, please hit "Accept." That is the only way I can receive credit for my answer. Thanks-