Hello M, thanks for posting your comment but I'm not sure I can provide the answers you are looking for but will try.
Any payment will be backdated to when the application was lodged.
I would be contacting your local member by letter, email or in person demanding but in a pleasant way for answers.
Another option is contact Vinnies, Salvos for food vouchers and I would be contacting Anglicare, they have contacts and can provide you with some relief, food as well as financial assistance, I know personally as they helped me enormously.
I realise his sickness allowance is important but can I also suggest that he books an appointment with his doctor.