Hi Emily
Thanks for your question. Have you seen a doctor to see if there are any underlying reasons for your low weight? I cannot stress how important is to check with your doctor first before making any changes to your lifestyle and diet.
You did not mention what symptoms you are experiencing at this moment that make you feel unhealthy, so I can only provide general guidance and need to refer you to see a qualified nutritional therapist to address the root cause.
Increasing the intake of vegetables to about 500g to 1kg a day would be a good start – some can be cooked (e.g. soups, stews etc.) and some fresh (smoothies, salads) to add a good variety of nutrients to the diet. Fibre is essential to clean our intestines to improve digestive health and detox hence aim to obtain at least 25g of fibre a day (using vegetables and whole grain foods). Avoid hydrogenated fats and oils (e.g. fried food, margarines, refined oils like Vegetable or Sunflower oil), fast food and processed/pre-prepared food in general, sugar and sugar containing products and processed meat (like ham, sausages etc.).
If you struggle to put on weight and not feeling well in your body, it could be due to food intolerances hence it would be useful to see a nutritionist that could help you to identify these and give you a guidance on what to eat exactly. We are all different and have different nutritional needs, so it is essential to get a personalised advice to fit you and your needs.
Good luck!