Wordpress - if is_plugin function?

So, I have been trying a couple of things but I can't figure it out.

In my header.php file I have a simple PHP line (custom-made Wordpress theme):

<?php if ( is_page('Home') || is_404() ||  is_search() ) { echo ""; } else { echo "<h1>". get_the_title() ."</h1>"; } ?>

This was working GREAT until I was required to install "The Events Calendar" plugin and adapt it to my theme.

The plugin allows me to go into its settings and create a URL slug, in this case I named it "reunions" and I did "reunion" slug for single events. So, logically I should be able to do this:

<?php if ( is_page('Home') || is_page('reunions') || is_page('reunion') || is_404() ||  is_search() ) { echo ""; } else { echo "<h1>". get_the_title() ."</h1>"; } ?>

These two attempts didn't work either:

$pagenow == 'the-events-calendar.php'

is_plugin_active( 'the-events-calendar/the-events-calendar.php' )

My work around would be to manually add <h1>(title)</h1> to each page, there's gotta be a way to do this. Any help would be greatly appreciated :)