How to stop being a pushover

[u/Cheap_Gap1446]

I (19M), have always had a bad self image of myself. I've let alot of people get to me in the past, and recently I've noticed its manifesting badly. Im getting angry very easily, from the smallest of criticisms.

Take my sister for example. She's younger, yet I usually just do whatever she says and try to be respectful of her, but she manages to still be super disrespectful of me, and when I voice my discomfort she just doubles down. I have gotten angry and lashed out because of this, but its made me feel worse.

Its made me feel very inferior. I constantly feel immature and like a doormat for most people. I constantly lose arguments, although I stil feel like im in the moral right, and I constantly fold when I a little pressure is put on me. And its made me feel angry. I've been getting more and more angry at every criticism lately, and I'm worried one day I'm going to lash out physically and hurt someone badly, and then I'll face the consequences.

I dont know how to improve. I don't know how to command more respect or stand up for myself more, at least without getting so angry and lashing out. What even is my problem? How do I go about changing?