Update 2018-02-18 06:12
If you're running Raspbian Jessie and you updated Pi-hole to v3.3, you likely ran into issues. This is because the version of dnsmasq that ships with it does not support the log-queries=extra option, which we use in v3.3.
You have two options to resolve this: revert Pi-hole to a previous version or upgrade dnsmasq manually.
Continued at Pi-hole v3.3 Released: It's "Extra" Special