If you've lost the USPS tracking number and receipt then there's not too much you can do to track the package.
To be able to track the package you need the USPS package tracking number because the USPS doesn't keep a record on file of tracking numbers.
But if you've paid for the tracking number at the post office they may have a copy of the receipt when you paid for the package delivery and added a tracking number.
If you don't have any record of the tracking number then there's no way of tracking it.
If you've looked up the tracking information online before then it might still be in the browser history so try typing in the USPS tracking url and maybe the tracking number will show up where you've previously tracked it if possible.