Fatal Error Please Help

Hi, I’m using the Mantra theme, and I really like it, but I keep getting this message:

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 44 bytes) in /home/content/40/10385640/html/wp-includes/wp-db.php on line 1545

My homepage does not load, but my other pages do. What should I do?

here is my site

thanks