DD welcome to Belly Belly and you are welcome to join the TTC forum - everyone was "new" once - you will be welcomed with open arms.

It's not unusual to have cycles that are a bit over the place after delivery - it can take some months for this to normalise. I lost 3 babies after 13 weeks and with all of my deliveries it took a long time to be "normal" again.

9mm is fine - depending on where in your cycle you are. It is also common to have a short cycle thrown in which may be what happened than your earlier than expectd fertile mucous.

Be gentle with yourself - take time to get to know your body again.

Again - I am so sorry for the loss of your son - sending you lots of love and a bg hug.