Storage space running out, some system functions may not work correctly

A

AC Question

This question has been asked a lot but none of the answers so far has helped me.
I literally only have 1 app installed on my internal storge, and its 12Mb big. But now this message appears "Storage space running out, some system functions may not work correctly", and i have around 10% space left. But the thing is I have an app manager than can move apps to SD and clear cache and I keep clearing the cache but nothing works. Is there anyway I can clear the system cache? Because my storage keeps filling up without even installing apps. Before I've had as low as 8% storage left for days but no message appeared, now I have +12% and the message wont go away...