Help Me?

I'm 17 years old now and i've been really depressed for quite some time, just having feelings of not being good enough. I find it hard to find excitement in things, mood swings sometimes i'm really happy, sometimes i'm suicidal. I have friends but i'm not entirely myself with them. For instance i show them a part of me, but the other is missing, deep down. I do show my humour well, but i can't show the heart of me? I go through times of just crying so hard that i have really bad headaches. A big part is just peer pressure. Even know i want to cry. I have no idea what i want to do in a career, i know i'd love to go traveling all around the world, and i definitely want to move. I feel like i don't enjoy doing the things kids my age enjoy to do, my friend just wants to go out all the time and meet people. But i just hate not being in my comfort zone, so i don't go. I do go out with a friend all the time, but when it comes to being with loads of people i don't know to well. I just clam up. I feel deep down i actually like the attention, but sometimes i find it so hard to express myself. It's making me suicidal, and i'm getting to the point where i feel like i'm losing myself. Any suggestions? I don't know how to tell my mom, if i say i'm depressed she will just think i've had a bad day or something, and i always get so sensitive when i talk about it and just cry. I feel weak when I cry.

Thanks...