How do I calm myself down? What's wrong with me?

Before 6th grade, I was never nervous and didn't embarrass easily. But since then, I have had the worst time giving presentations: my voice would tremble and within seconds, I'd break down with laughter. I'm now in college and it's been getting worse, not with stage-fright, but with attractive people, specifically girls (I am a closet lesbian). My self confidence is pretty low so whenever I talk with them, I constantly believe the worse like what they are thinking about me. Then I stutter at times and my face twitches weirdly.. How do I stop the twitching.. why does it do this. One way I calm myself down is run, but I can't run every time I'm about to meet someone. What are some alternatives? What's wrong with me. Oh also, I secretly have eating problems so does it have anything to do with nutrition?

You have a form of anxiety something went wrong with me at 11 im a bi-sexual & I do studder but not often & I havnt even met anyone new really since except a few teens but this town is small & shit.. You have the same thing I have except I walk in a room & feel scared or really anxious your twitching is probably worse then mine I twitch or look & talk to someone & feel like everyone around me is staring at me but only sometimes where are you from though can I ask? Your a closet one in what way do you mean that I am actually 15 & ive been dealing with anxiety & depression for a long time..