Cannot modify header information – headers already sent by (output

i recently updated my site to the latest version of WP and the latest version of my theme (porcelain)…it has been buggy. so i deactivated all plugins and reactived one by one – long story short, the site was working decently (for a day or so).

now i get this error:
Warning: Cannot modify header information – headers already sent by (output started at /home/sheinnovates/www/www/index.php:1) in /home/sheinnovates/www/www/wp-includes/pluggable.php on line 1121

i’ve looked at other strings within the WP forum, but i don’t want to change my php file (as i’ve read to do) and mess everything up (i’m no pro, obviously).

here is my line 1121 in pluggable.php
header(“Location: $location”, true, $status);

(there is a blank line before (1120) and after (1122).

as well as this error – there is a weird “choose file” / submit in the top corner of my screen when i try to login into site via wp-admin