you can't laugh on command. It doesn't work that way. Just be yourself, if something makes you smile, smile, if it makes you laugh, laugh. ...
However, those thoughts you have are very normal for a 13-year old. At that age you enter adolescence, you start having inferiority complexes, lacking identity.
It's all very normal...
My guess is that you don't really feel comfortable around your friends...you're trying to fit in.
...