php - What can I do about exhausted memory on Wordpress while developing via a local Ubuntu server?

Some short facts first:

• Ubuntu 16.04 LTS on VirtualBox with 4096M ram.
• PHP 7.0.22
• Wordpress 4.9.2.
• macOS 10.13.2
• Using a shared folder to access my websites via localaddress.vm/[websitename]

I have set up a local Ubuntu server via VirtualBox to not having to use MAMP anymore. I develop Wordpress websites. Frontend of the Wordpress website is all good. /wp-admin is also playing nice but after successfully logging in, I am not getting redirected to the Dashboard. Instead I get the following error:

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to 
allocate 262144 bytes) in /media/sf_sharedwww/thermoshield/wp-
includes/functions.php on line 1872

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to 
allocate 262144 bytes) in Unknown on line 0
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Tried solutions:

• Upping the RAM on my VirtualBox
• Upping the memory_limit for WP viawp-config.php
• Upping the memory_limit via thephp.ini file.
• Basically the first page of Google results

Please help, I cannot continue development if I can't access the back-end of Wordpress.