Anybody have any good tips to keep smiling without thinking about it.

Thing is that when I relax my face, I feel that I somehow look scared, insecure or even angry.

So I have tried to smile more, and have really got great response from people around actually.
However it feels like I need to remind myself to keep smiling even tho I'm happy "inside".

And this feels uncomfortable somehow and I feel it "takes energy" and focus from me.

Tips and suggestions wanted! :)