Database [Q] Internal memory becoming low whenever i clear cache


I'm using Xperia M (Android 4.1.2). I used to free up space in interanal memory by clearing cache and whenever i cleared cache memory will get freed. But now for some apps if i clear cache internal memory remains the same or sometimes free memory will decrease instead of increasing. Can anyone explain y this is happening? I'm clearing cache from the Settings itself, not by using any app.