Hola Amigo
I can help, I once volunteered at a youth centre where I mentored a girl who was a compulsive liar and she was EXACTLY like you, she went to a middle class school full of beautiful children, she was plain and poor and she lied compulsively about everything.
I don't know if you realise but people know your lying, they'll never mention it to you however they mention it within each other, they do realise sometimes that your lying, they will feel sorry for you and not mention it.
You suffer from low self esteem, low self confidence and grandiose delusions and compulsively lie to create an image you so badly wish to possess to the extent where it takes over your life and you can't go back. If you are more extreme you could possibly be suffering from Narcissistic Personality Disorder or Histrionic Personality Disorder however I doubt you have gone that far, read up on it and look into the symptoms.
Start by picking one thing that you know you always lie about. For example: your weight, your age, how you got that scar, what you do for a living, etc. Focus on telling the truth about that ONE thing EVERY TIME. This will give you practice and get you used to answering honestly. This is especially helpful if you pick something that comes up frequently in conversations. Have the honest answer ready in your mind, repeat it to yourself if you have to.
I think once you have identified what you lie about most you will continually repeat the truth and tell yourself that your are fine just as you are.
I would drift away from all the people you have lied to as many of them will not give you their trust again and start forming new relationships with people who you tell the truth with the from the start.
Research Sam Vaknin, compulsive and pathological lying and the two personality disorders I stated earlier and get to the bottom of WHY you lie so much, you have alot of shame, low self esteem and don't feel you are good enough, you need to build that up.
Therapy can sometimes help you answer questions as to why you do certain things too.
Good Luck!
xoxo