Weblog Database

I have a wordpress blog related to health niche and have 5000+ posts and 12000+ tags and 50 categories.



The blog worked great untill a month back. Now, whenever I update my old posts or access old posts, the mysql usage goes to 100% for few mins then works. Because of high CPU usage my host blocks my account. There is no resource issue if I create a new post or view new posts. The problem is with old posts only.



I also did DB optimization, exported the DB and imported to new DB, changing themes, disabling plugins, etc. but the problem is not resolved.



Anyone have had experience like this ? would love to hear your suggestions.



Using latest WP versions, latest version of plugins.