I'm sorry to hear you don't like yourself. I was definitely in your position when I was younger and learning to love myself has been a long journey.
Loving someone, including yourself, is a choice you make everyday. Positive affirmations can really help, look yourself in the eyes in a mirror and say 'I love you'. You can even do a meditative practice where you repeat "I love me" over and over in your head or aloud. You need to fake it to make it here. Try to lessen your negative self talk.
It would be helpful to look at what contributes to your low self esteem. If your relationships are negative it will really bring you down, but if that's too big to deal with right now just focus on yourself.
Start moving, find an exercise you enjoy and will stick to. Walking is so beneficial. Use this moment to try out any type of exercise, I love yoga, you might like jiujitsu! Make it into an adventure to find your thing. There's loads of great home workout plans to. Try to make healthy choices with your food but don't put too much pressure on yourself.
Something that makes you look so much better is fixing your posture. There's a course by Karina More called Marathon 1 which focuses on posture and anti aging facial exercises. I've almost finished it for the 3rd time and it works so well. (I'm not affiliated, but it's worked for me).
Start saying yes to things! Tell yourself you have to say yes to invites unless you have a very good reason why you can't.
What did you enjoy when you were younger? Did you like drawing, writing, games, dance, music? You need to find something that brings you joy.
You deserve a beautiful, happy life and to be the best version of yourself. Good luck xx