Is my website hacked?

I have been getting ‘500 internal server’ errors sometimes when i try login to my admin area or when saving a post,page,widget etc. I re-installed wordpress,deleting everything but a few days later the same problems occur. Could my have been hacked? Below is the error i get.

PHP Warning: strpos() [function.strpos]: Offset not contained in string in /home/anasika/public_html/mywebsite.com/wp-includes/js/tinymce/plugins/inlinepopups/skins/clearlooks2/img/537.php(3) : runtime-created function(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code(1) : eval()’d code on line 1 [31-Oct-2012 00:02:22 UTC] PHP Warning: gzinflate()