If your package has been marked as shipped, please note that it actually has been shipped and just not scanned at the facility. Sometimes USPS loads packages straight into their trucks to the target destination and skip the scanning process. As I ship via truckload my USPS carriers do not scan each package given.
USPS Media mail will sometimes have books stuck in transit for a good amount of time. With a heavy heart no action will be taken until at least 1 month has passed. This is because I will send out replacements after 2 weeks and on the 3rd or 4th week the original package is finally out for delivery.
If you concerns about packages being stuck in transit for awhile please Opt-in for UPS shipping otherwise no action will be taken until 1 month after inactivity.
Last note, international shipping may get charged with customs/ import-taxes. So please be aware of this when placing international orders.