How do I stop thinking that I need to eat less when "less" is already not enough?

Tell yourself that you need the nutrition. You have to eat an amount that will keep you health, and if you're barely eating that can do horrible things to your body. You may feel full after a few bites, but you have to convince yourself that its the right thing. It's easier when its healthy things, like fruits or vegetables that you like. Eating more (especially when they're healthy and delicious, my personal favorite is strawberries) will make your body feel better and hopefully you can stop thinking about eating less, and thinking about eating well.

That's a tough one. Figure out what is standard amount of food for someone your age or gender, you can look at the food guide or see a nutrionalist or google search this info, then compare it to how much you eat.

Well, you could try and start telling yourself repeatedly to eat more, until you start to believe yourself.

You need to research how underweight you really are. And then look up anorexic girls and think how horrible they look and how unhealthy they are. Eating less is such a terrible problem with people and it is so unhealthy. Eating less means you are unhealthy. Maintaining a healthy balance and weight is healthy and normal.

You only think that you need to eat less when you have been eating too much. Other than that eat till you are full then stop. Overeating is also bad for you.

You need to focus on what you already to eat. Realise how little you eat and notice how bad it is for you. Ask yourself why you feel this way? It seems like you're frustrated with weight. Perhaps seek help from a professional and speak about your struggles with food.

This is probably different for everyone, but one thing that helped me was thinking about how I would treat a pet or a friend. If feeding an animal that much would be abuse, feeding me that much would be abuse. It helped to think like that at first so that I could see food as fuel and not as an enemy.

Get yourself into the habit of goal making for so many calories a day aka 2,000. You would still be in total control, but then you would meet your personal goals that you set.

Workout that will help you lose some weight and eat healthy food that will help you lose weight.