When people look at me i act weird?

Okay this is really weird, when people look at me, when i'm telling something serious or even when people look at me my mood changes my face starts to tremble and i have to keep it straight (its very hard) but it looks like im about to cry and i am. When i tell something sad my face trembles or if people laught at me im gona cry why is this is it weird how can i stop?