It sounds like you may be running a plugin that stores too many transient options. If you can’t currently access wp-admin, try FTP’ing in and renaming your /plugins folder to disable all plugins. Then you should be able to log in to wp-admin. Next, back in FTP rename your /plugins folder back to the normal /plugins, and leave all of the plugins deactivated in wp-admin.
From there, go into phpMyAdmin and view the options table. Go to the last few pages and see if you notice any patterns – you may be able to tell which plugin is storing too much in the database, and then the solution is to remove the plugin and replace it with an alternative if you really need the functionality. Once you’ve found the culprit, run WP-Optimize ( https://wordpress.org/plugins/wp-optimize/ ) to clean up your database and reduce its size. It’s a great plugin to run on a regular basis to keep things running smoothly.