If PP didn't know you had moved, because you forgot to correct your address, and you did not purchase a Mail Forwarding service from the Post Office, you have to your own legwork.
Go to your old address and ask the new tenants if they have received any mail for you. They may have it still hanging around, with the intention of giving it back to the PO. If they are helpful, give them your new address.
If they have given it back to the PO, go to your usual outlet and ask if they have anything for your in their Undeliverable drawer. This is not likely since most outlets don't like to have stuff cluttering up their limited space.
If you purchased Mail Forwarding and it has run out, you should be aware at this time of year that you may not have received all the paperwork for your income tax.
