Warning Message: cannot modify header

Hello,
This morning as I have been working on my blog all of the sudden my changes were not able to modify because I got the following message:

Warning: Cannot modify header information – headers already sent by (output started at /home1/mommyhp2/public_html/wp-content/themes/truly-minimal-wpcom/inc/custom-header.php:10) in /home1/mommyhp2/public_html/wp-includes/pluggable.php on line 1179

Now that is what comes up when I try to open my site! Even when I try a private window or another browser.

I had installed the Icegram plug-in right before this happened. Did that mess something up? I have no idea how to fix this.

Mommyhomemanager.com