Try this code for forcing HTTPS:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L,QSA,NE]
Your complete .htaccess:
# For security reasons, Option followsymlinks cannot be overridden.
#Options +FollowSymLinks
Options +SymLinksIfOwnerMatch
IndexIgnore */*
RewriteEngine on
RewriteBase /
# if a directory or a file exists, use it directly
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{HTTPS} off
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L,QSA,NE]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# otherwise forward it to index.php
RewriteRule . index.php