My tracking hasn't updated since Miami, Florida. Is it lost?

Most likely, not.  That's a terrible answer, sorry, so I'll try to expand.  Most international packages go through the port in Miami, Florida (or sometimes Jamaica, New York).  Sometimes, they only show it Arriving in Miami, and sometimes they'll actually show it Departing.  That is as far as USPS will update, and any other updates is dependent on the receiving country.  I think about 90% of countries do not show further updates, and some countries will not even recognize the USPS tracking number as valid.  However, your package is likely not lost, as over 99% of the packages we ship out make it to their final destination, safe and sound.  Please remember that the quoted time frame for international packages are 6 days - 6 weeks for First Class, and can actually take longer during congested holidays such as around Christmas season or Chinese New Year.