启用网址重写规则时的联系表单重定向

i made a form contact with header Location redirection after form validation. Every things works fine when url are like this

mysite.com/index.php?p=contacts --->> with

header('Location: index.php?p=contacts'); in post_contact.php

but afer adding this rule in .htaccess,

RewriteRule ^(en_US|fr_FR)/([^\?]+)$ /index.php?lang=$1&p=$2 [NC]

redirection in post_contact.php doesn't work anymore

header('Location: index.php?p=contacts');

may someone try to give me some help