Are you looking on eBay or at USPS?
eBay are having many issues keeping in sync with USPS.
If it hasn't total disappeared (never made it back to the PO because the carrier dropped it somewhere) it should be scanned, probably at the destination regional facility or the delivery post office and failing that at delivery.
As far as what to do, stop looking at the tracking for a few days and don't worry about it unless you hear from the buyer.
I know you are not in the worst hit area for snow but it certainly has affected service at many of the regional sort facilities nearby.
Paranoia strikes deep
Into your life it will creep