Hopefully this is of some help: USPS shipments overseas go
through several processes, especially if they don't use Priority USPS. It's very common for packages to be held over for weeks on end for customs purposes (especially if they are liquid shipments).
While you can't do anything about the USPS, you can request that the person who shipped it calls them and questions what's going on. Please don't take this out on the person who shipped it, as there's little they can do once the package has left their hands. The usps will take up to 45 days to respond to international shipment questions.
What you can do is contact your local post office and explain the situation and they CAN file with the USPS to figure out what is going on, or let you know if they have it held up on their end.
My recommendation for overseas shipments: Always get either USPS Priority or better, or use another carrier service. USPS First Class international is really hit or miss, and I've seen so many packages held up for 40-days or so because of it.