can't get passed the mental part of it all

In High School, I always skipped breakfast and lunch because I was afraid of getting "big." What finally scared me into eating more was my Health Class. We started talking about eating disorders and the teacher said that "if you don't eat enough food, your body will start eating away your muscles---which could include the lining of your heart, etc, which could cause potential health problems down the road."

NOW, I am not a fitness expert or anything like that so I don't know how true that is, but it scared me so much. After that I began eating more. I didn't want my body to start eating away at my organs---especially the lining of my heart. Hopefully, just thinking about what you are doing to your body will make you want to start eating more...

Instead of overwhelming yourself (and likely your body since it's used to low calories), why don't you make it your goal to add 1 thing a day to increase your calorie count? You'll be able to build up food items/quantity over time and your anxiety over gaining will be limited. Feeding yourself properly is the only way to truly lose weight.

It's possible that the source of your anxiety is deeper than just eating and exercising. I'm guessing that there are probably certain triggers (sources of stress) that cause you to become overwhelmed and thus obsess on your weight. I'm sure that all the pressure at school has been heavy on your emotions, so I can see why you would be afraid to gain weight.
What things in your life make you the most worried, in general?

By no means do I want to scare you, but from everything you've said, it's possible you're at high risk for this to become a serious issue. Particularly if you are still an adolescent (under 25), you should be eating at the VERY minimum, 1200 calories every day. So, I don't want to overstep my boundaries (and apologies if I have), but I think the obstacle is most likely an intense fear of rejection. A solution for this is converting that fear and the negative thoughts about gaining weight into a motivation to be healthy and confident.

Here is a tip: Start out by trying to change the way you think by changing the things you say to yourself in your own mind. First, keep a sheet of paper with you, with a line drawn down the middle of it. When you start to feel overwhelmed, write down what fear you are feeling (i.e. "If I eat 1200 calories, then I will become fat, and no one will like me") on the left side. On the right side, write down something positive, encouraging, and motivating "If I eat 1200 calories, then I WILL be a normal, healthy, strong young woman, and people WILL like me"). When you've written them all down, cut the paper down the line, take the left side and burn it, throw it away, flush it, etc. When you do so, tell yourself (in your head, or out loud) "I am beautiful, I am healthy, I CAN do this". Then, cut out each of the statements you've written down on the right hand side. Keep one in your wallet, by your bed, in your purse. When you see them, read them to yourself (again, in your head, or out loud). Make a habit of saying them every time you wake up, before and after you eat, before you go to school, when you come home from school, when you work out, before you go to bed. Any time you start to feel overwhelmed, repeat one of those positive statements to yourself. It is normal, at first, for you to question the new statements, but with repetition, you will start to change how you think about this difficult process.

Again, sorry if I'm saying too much. I realize how INCREDIBLY frustrating the social/peer pressure toward thinness is, ESPECIALLY during the adolescent years.

okay it seems to be a mind barrier that is there for a lot of people on here.

MFP set my calorie limit to 1200 and that was just stupid.. I raised it and I started losing more weight. Your body is most likely in a starvation mode at those calories. What you need to do is eat more food, but foods that promote a healthier metabolism. This could result in a short term weight gain but once you get past that and your metabolism starts to fire up then you can start eating more and you will notice the weight falling off.

I honestly suggest doing some research, look at other peoples diaries and see where you can add calories and healthy fats and so on to promote a healthier metabolism.

As you say, it is a mind barrier, so you may struggle at first but once you get those calories up and start eating more and seeing the weight fall off you will be happy you did it. It will also leave you feeling more energised and healthier.