You must specifically request that your Carer's Allowance claim is backdated, and you must have satisfied all the rules for claiming Carer's Allowance during the backdating period.
You can also challenge a decision not to backdate Carer's Allowance if your request is refused.
Carer's Allowance is paid into a bank or building society account either weekly in advance or every four weeks.
You can make a complaint about a delay you experience.
You can also ask for an interim payment of benefit, which you'll get if the DWP believes you're entitled to some benefit but it's not possible for the claim to be dealt with immediately.