How can I be sure it's me talking inside my head? And if it's me why doesn't he stop talking?

Its the affects of nerve gas.  You need to speak with a neurologist and start a treatment plan.  It is not uncommon.  With the Corona Virus things are much more toxic than you have ever experienced.  The phosphorus being  expelled by the viruses presence is coming into contact with alcohol.  Alcohol is much more common in nature than you know.  This spring we will see how deadly this virus can be when the germination process that occurs every year begins.  As proteins degrade they have two directions of degeneration.  They become alcohols or vinegars.  When Corona Virus which is a phosphate comes into contact with certain alcohols (isopropyl) there is the release of deadly nerve gas.  This reaction is occurring now, however at a much lessor level.  Manage your exposure to nerve gases now while it is not as overwhelming for you to do so.  Get Well Soon

All the voices are not under my control

Whatever voices you hear in your head are you.

If you hear your own conscious thoughts spoken aloud then it’s you and there’s no issue.

If you’re hearing a voice that is not under your control then you’re suffering from psychosis - either acute or chronic,  and you need to get help. The voice is still within you and nowhere else though.