If you have been charged, this means that police have concluded – rightly or wrongly – that something about your incident took it outside the parameters of self-defence.
Self-defence does not apply to every conflict or assault; it is not a protective shield for every time you are involved in a physical altercation or provoked to engage in one. Perhaps surprisingly, it does not even cover all situations in which you may have been assaulted first.
There is a strict legal threshold for what constitutes self-defence.