Cannot log into my own site

I get this error message when I go to the log in page on my site.

Warning: Cannot modify header information – headers already sent by (output started at /home/sewingmo/public_html/itsmyimagination/wp-content/themes/oh-so-very/functions.php:11) in /home/sewingmo/public_html/itsmyimagination/wp-login.php on line 12

Then, I get this when I do log in and I cannot get into my site.

Warning: Cannot modify header information – headers already sent by (output started at /home/sewingmo/public_html/itsmyimagination/wp-content/themes/oh-so-very/functions.php:11) in /home/sewingmo/public_html/itsmyimagination/wp-login.php on line 12

Warning: Cannot modify header information – headers already sent by (output started at /home/sewingmo/public_html/itsmyimagination/wp-content/themes/oh-so-very/functions.php:11) in /home/sewingmo/public_html/itsmyimagination/wp-includes/pluggable.php on line 369

Warning: Cannot modify header information – headers already sent by (output started at /home/sewingmo/public_html/itsmyimagination/wp-content/themes/oh-so-very/functions.php:11) in /home/sewingmo/public_html/itsmyimagination/wp-includes/pluggable.php on line 370

Warning: Cannot modify header information – headers already sent by (output started at /home/sewingmo/public_html/itsmyimagination/wp-content/themes/oh-so-very/functions.php:11) in /home/sewingmo/public_html/itsmyimagination/wp-includes/pluggable.php on line 331

Please help, I have no idea what to do and cannot get into the site to check for problems.