The outside doesn't match what's inside...

I smile on the outside, sometimes even laugh, or even speak in a light, sing-song manner when I don't feel that way on the inside.

Actually, I'm just now beginning to become aware that I don't feel that way on the inside. I used to think that I was someone who could see the humor in any situation - and even tell others about it and laugh.

I have trouble in my interpersonal relationships, having only about two people are somewhat close to me. Both have noticed that I do tell them such sad stories and I'm smiling when I do it; the other day when one told me this I noticed that it was because I was about to cry and wanted to stop myself from doing so (embarassed to do so because of what I'll look like, I'll seem to weak, like I'm not all together, etc). I once was mugged years ago, and when I told my "friends" at that time (I was actually living with them and it happend a few blocks outside of apartment one night) none of them believed me at all... and it made me feel so terrible then that we're no longer friends now. The reason that they gave me was that I was making it all up since I was like, "Hey guys! Guess what!?" and was smiling and seemed excited when I was telling them... I actually felt shocked/scared and a little embarassed.

The psychologist I'm seeing has also pointed out that I tend to do this as well - but I've only had two sessions with her. She will also ask me, "When you tell me these things... are you feeling how you feel, or are you just telling me?" The truth is, in that session I was telling her things without feeling. When I would stop and try to think about how I felt by paying attention to my body, I felt nothing... just like I was there and contented.

What is this called? And where can I find more information on it (any good sources out there)? And what can I do?