It seems all to apparent to me, by the content of your post, that you are not familiar with what the Holy Ghost is. The Holy Ghost is the third member of the Godhead. He is a Personage of Spirit, a Spirit Person, a Spirit Man, a Spirit Entity. He can be in only one place at one time and he does not and cannot transform himself into any other form or image than that of the Man whom he is, though his power and influence can be manifest at one and the same time through all immensity. He is the Comforter, Testator, Revelator, Sanctifier, Holy Spirit, Holy Spirit of Promise, Spirit of Truth, Spirit of the Lord, and Messenger of the Father and the Son, and his companionship is the greatest gift that mortal man can enjoy. His mission is to perform all of the functions appertaining to the various name-titles which he bears.
Most importantly here, he is an influence. That means that if you heard him as a voice then the voice was all yours. He communicates using concepts, feelings and emotions, which is why his communications are so super fast. His influence fills the immensity of space. As worthy children we can tap into that influence and receive knowledge, even hidden knowledge. His influence can answer any and every question we have to ask, however, the answer, for me, has never come by the spoken word, whether in my head or through my ears. There simply is no comparison between voices in your head and the influence of the Holy ghost. One can never be confused with the other. They are both separate and distinct. It certainly can never be mistaken as the normal function of the brain as the source is always external and enters you mind like a wave of energy.
No, you were never a Christian. If you were converted by the Holy Ghost, testifying to your soul, then you would still be a Christian today. There is no going back. It is a virtual impossibility to deny the influence of the Holy Ghost once experienced. Secondly, I know that voices in my head is not the Holy Ghost. I would worry that I was a schizophrenic if I started hearing voices. The Holy Ghost is an influence in a conceptual form.
4 And when ye shall receive these things, I would exhort you that ye would ask God, the Eternal Father, in the name of Christ, if these things are not true; and if ye shall ask with a sincere heart, with real intent, having faith in Christ, he will manifest the truth of it unto you, by the power of the Holy Ghost.
5 And by the power of the Holy Ghost ye may know the truth of all things
Notice that he will manifest the truth not speak it.