I was only in a new job for 4 months when diagnosed. I thought I would be able to work through my chemo treatment but physically and mentally I just couldn't do it. I was devastated and felt very guilty about not working. ..but I accepted I did need to do what was right for me.
Are you a casual? Nobody can fire you for extended sick leave and there are workers rights to cover you for that. Just provide the regular medical certificates about fitness for work.
https://www.fairwork.gov.au/leave/sick-and-carers-leave/long-periods-of-sick-leave