some practical solutions: make a little skincare routine, dress in clothes that make you feel good, exercise (doesn't have to be gym - you could take up cycling or hiking if you haven't already), give more to others and do other stuff that will help with your unfairly low self esteem. attractiveness consists of 3 parts: health, hygiene and a reasonable amount of confidence; it doesn't matter if you're naturally the ugliest person in the world, as long as you look after yourself and others, people will see the good in you.
emotional solutions: learn to care less, look beyond the superficial of good looks, value things that are genuine and wholesome.
i know exactly how you feel though; when i go out i'm so conscious of other people - i want to hide away from their judging glances, when in reality, strangers don't care about my face, and even if they did it wouldn't matter to me - i don't want to impress them, i want to impress the people i care about instead. just know that self-esteem is something that fluctuates in everyone and be grateful for the things you do have. you are worthy of love, no matter how bad you think you look.
“More disturbing than hurt is love when it's wrong.”
― Ali Land, Good Me, Bad Me