How do I stop overeating when I'm eating alone and stop undereating when I'm eating with other people around?

There are many ways you can reduce the amount that you eat, you can restrict what you have available in your pantry and home by simply not buying foods that you know you will overeat on, such as chips, lollies and chocolates. You can prepare meals in advance by putting them in containers and putting the correct portion size. When eating around other people, you need to relax, don't overthink what you will be eating, or don't think about gaining fat or weight, you won't as long as you eat the correct sizing.

You might be overeating alone because you didn't eat enough when you were with other peaople. The best way to overcome this is working on the reasons why you do these things. You have to search for the reasons why you overeat, and why you undereat, and then try to solve them.

You can sit a chart up and show your self a health main plain and serving size chart to work of for a while until you feel you can handle it solo, then by then you should be able to make a one person serving size plate

There's an imbalance here. You need to make yourself stick to eating an appropriate portion, use will-power and self-discipline. When you stick to doing this, you will eventually balance things out.

Use distraction tehcniques to stop yourself overthinking things. Set yourself little targets: eat a sandwich and yoghurt for example only, no more; no less.

When you are eating alone, try to give yourself a certain portion of food before you sit down and eat it. Put the rest away. As for eating with other people, try to get a supportive friend/relative/trusted adult to spot you during your meal. For instance, before the meal try to ask them to watch over you as you are eating and to check in/ encourage you to eat more and fulfill your goal for that day.

Knowledge yourself about correct portion sizes and learn to eat all parts of the food groups. It is not uncommon to eat less when with a group, but you know whats right for you and always eat until you are comfortably full. Don't less others intimidate you while eating, eating with friends is supposed to be for the social aspect.

Maybe you could try a helpline? I myself have experienced this, and i found that a helpline helped.

Maybe try to figure out how much food you need for your height and make a schedule. Don't make it to strict or stress over it, but try to follow it. An example could be "Morning: 2 eggs and OJ. Afternoon: Serving of spaghetti and meatballs. Evening: Chicken Curry. " Make sure you eat whether your out or not, and have no exceptions. You could also make a list of snacks and have 2 or 3 a day, depending on what you want. Hope this helps and don't beat yourself up about it!

This sounds like disordered eating behavior and would best be helped by speaking to a professional! You deserve to get help now, so that you can heal!