OJS 2.4.2 Getting slow and can't input DOI (only in one journal, other journal everything normal)

I am using OJS 2.4.2 to manage 23 journals, but only 12 journals that currently active. The question is, when I open a menu and input a form in one journal that have only some submission, the menu seem normal. But when I click a menu in another journal, that having many submissions in review, the menu getting slow. And also in this journal, I can’t input DOI with this error:
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 72 bytes) in …data/ojs/lib/pkp/lib/adodb/adodb.inc.php on line 818. But when I input DOI for other journal, everything normal.