Where a knife is used to threaten or cause fear, the Magistrates' guidelines state that the offence is at 'Level 3' and must therefore be referred up to the Crown Court, as the appropriate sentence should be above 6 months. (That can happen even after the case has initially been heard in the Magistrates' Court , when the Magistrates realise that their sentencing powers aren't high enough).
If (as the above suggests) the matter is eventually heard before the Crown Court, your injuries would be regarded as 'low harm' but the use of a knife would count as 'high culpability', making it a Category 2 offence. The starting point' sentence is 26 weeks imprisonment. There would be a one third reduction in that sentence because of the guilty plea but that would probably be cancelled out by the previous convictions, which would push sentencing up again.
So, despite the fact that the use of a knife is meant to result in a sentence in excess of 6 months, an actual sentence of around 6 months would seem to be likely (with half of that time actually being spent 'inside').
Chris