Please verify your order actually shipped via USPS and not via another carrier like UPS. You can confirm this by reviewing your shipping notification. The second line begins: "We are pleased to let you know that your order shipped on DATE, via..."
This section will clearly indicate which carrier your order was shipped through.
Please note it can take up to 48 hours for USPS to update the tracking information once it ships from our facility. UPS and FedEx shipments usually show accurate tracking information within 24 hours.