Just a stick in the mud?...

OK, something is bothering me. I think people think I am sad all the time. Maybe I am and I'm just used to it and I don't realize I am sad. My kids (at school) have made mention several times recently that I don't smile very often. My assistant principal seems to have asked me a lot lately why he never sees me smile. Brad is always telling me to smile. Does anyone else think I seem like a miserable person? I mean, I do have a lot on my mind usually. And I generally don't like my job, but I thought I was better at hiding that than I apparently am. One of my kids saw me while I was out to eat with some friends and she heard me laugh. She said she had never seen me smile or heard me laugh. How pathetic is that? I know I need to loosen up and learn to have more fun, but I honestly didn't think I was THAT bad. Help!!! I need to loosen up!!! I used to be fun. What happened to me???