Sick?

I'm beginning to wonder if my depression is associated to my social habits.
I used to think it was because of my health because when I suddenly no longer have an appetite for anything and stop eating I get depressed but I think the root of the problem is that even the smallest things that happen to me affect my mental state.
For example, if I feel like I should have said hello to someone but I didn't then it bothers me all day long and ultimately I'm in a really guilty, sad mood for the longest time just because I didn't wave and smile at someone.
Or if in class, no one sits by me I feel isolated and alone for the rest of the day. If I say something awkward or stupid then I feel self-aware for the rest of the day and I think it's all this kind of stuff that is affecting my mental health and also my physical health.

This whole week, I have not been able to eat in the dorm's cafeteria. The moment I step foot in the cafeteria, any appetite I had disappears. Today, I didn't even go down there because I was so anxious about it.
And today, I have been having the worst thoughts I have had in a long time. And when this happens I suddenly have no fears and do things that I really wouldn't were I in my right mind.
Today I kept thinking,over and over again, that I want to try a cigarette. I'm 18 so it is completely legal, so why not, right? I love the smell of smoke; I always have. But if I start I may become addicted. But I keep telling myself that isn't a bad thing, even though I know it is.
I even thought, legitimately, about considering getting a tattoo. I thought, "THAT is a great topic of conversation. Great way to make friends."
Then I thought about trying hookah. It's also legal so why the hell not? It smells amazing when I walk past the hookah bars and I think I would really like it. But I know I SHOULDNT I just somehow have no fears when I'm in this state.

Things like this have been occupying my thoughts lately; I just want to do something fun and forget about all the things wrong that I have done. I'm embarrassed with myself most of the time and I hate not being confident. Today was one of the worst. No plans, no one to hang out with...my friend didn't seem to want to talk to me...and I just sat there and scrolled through facebook, looking at everyone else's wonderful Saturdays..............

I'm beginning to think there is literally something /WRONG/ with me.
Like, why is it that I am so ill?

This happens too often, where I get sick, don't have periods for months and months, get depressed, tired all the time, no appetite, guilt and embarrassment....why does this happen?
Is it something I am doing to myself?

I honestly don't know. But it bothers me and I don't see how anyone would want to befriend someone like me.

Well anyway,
time to watch kdramas. <3