>I smile, laugh and look very cheerful on the outside
>inside of me I am a very sad person
>Isit that I am just good at hiding my feelings ?

Sounds like it but you arent hiding them from yourself. I actually understand this problem as I did it myself for years. You can run but you cant hide is what some people say.

What would make it easier for you to open up? Have you thought about why you dont open up? Is it something you fear? Or something else?