(UNDIAGNOSED!!!) Seasonal Depression Comeback?

So like the title says, I am not diagnosed with depression! Let me explain though. Every year towards the end of November into December, a wave of sadness, suicidal thoughts, and thoughts of self harm randomly come back. I (usually) am fine all year until these last months of the year start to come. It was early this year, at the beginning of November. I recently quit self harm and I'm afraid I might start again due to my undiagnosed seasonal depression. I can't go back to cutting my self, I want my scars gone. Anyway in short form, these next few weeks and months (sometimes lasts till summer), will be the absolute worst, so yeah... Thank you forr taking the time to read this!