When to register as a sole-trader confusing!!

I have only recently started taking on some freelance IT work. I was first paid in Nov-18 and after that in Feb-19. I have expenses as well which almost negate the income (income has been well less than personal allowance). I know i dont have to pay tax on this but do I need to register with HMRC?

if yes then when do I need to at latest? and when I need to send self assessment? Is it 5th April or 5th October? Very confusing!!!

Thanks