Difficulty setting up CiviMail on Bluehost
Your cron script may not work as displayed because $PHP is not defined, and because PARAMS= -j -smydomain.org -u mailsender@mydomain.org -p xxxxxxxxxx -e Job -a process_mailing will not define $PARAMS without quotemarks surrounding the variable value (instead you get a *sh error).

I suggest adding a MAILTO line with your email at the top so you receive the error output - this will help you debug if/when it fails.

MAILTO=you@example.com


I suspect that your website is not hosted at /var/public_html on Bluehost also? Might want to double-check that value, you might mean ~/public_html

Try this, amending values to suit your email/website?

MAILTO=myself@example.org
PHP=/usr/php/54/usr/bin/php
CIVI_ROOT=~/public_html/mydomain/wp-content/plugins/civicrm/
PARAMS=" -j -smydomain.org -u mailsender@mydomain.org -p xxxxxxxxxx -e Job -a process_mailing"
*/5 * * * * cd $CIVI_ROOT; $PHP bin/cli.php $PARAMS