I feel like I'm going mad and I don't know what to do. Although everyone thinks I'm always happy deep down I feel like killing myself. When I tried to talk to my friend it just all seemed pathetic and I ended up laughing it off and feeling ridiculous. I feeling like I can't breathe sometimes because I just feel so overwhelmed by sadness.

You are not going crazy. You are not alone. I'm sure you've probably heard this before, but what you are feeling is real and you are not being ridiculous. Please, go and see your doctor. He/She will be able to help you.