Empty your Safari cache more often. Go to your Safari menu bar, click Safari > Empty Cache
If that doesn't help, back to the menu bar, click Safari > Preferences > Privacy.
Click: Remove All Website Data
Quit then relaunch Safari to test.
If that didn't help either, open the Finder.
From the Finder menu bar (top of your screen) click Go > Go to Folder
Type this exactly as you see it here: ~/Library/Caches/com.apple.Safari/Cache.db
Move the Cache.db file to the Trash.