When using nginx as a reverse proxy all IP Addresses in your logs will be the same as the downstream server will only see the connection from nginx. To fix this you need to make a few changes to your nginx config.
Add the following to your nginx config for the domain/site you are using.
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header x-forwarded-for $proxy_add_x_forwarded_for;
Once the code is added nginx should pass along the IP Address of the user to your downstream server via the x-forwarded-for header as long as your downstream server supports that header.