Is it possible for asexuality to be caused by extremely low self and body confidence and shyness, being so scared of sexual intimacy that I can no longer feel sexual attraction to anyone?

Asexuality is a self-defined orientation embraced by individuals claiming it. My heterosexuality wasn’t “caused” by anything. It simply is.

Low self- and body confidence along with shyness are phenomena that can apply to any sexual orientation. Fear of sexual intimacy that impedes preexisting sexual attraction is an issue that doesn’t apply to asexuals since they don’t have it to lose in the first place.

Your question could posit the same thing about gay, lesbian, bisexual, queer, and pansexual individuals and the conclusion would be the same: body image, personality type, and sexual intimacy are issues that apply to most people. It’s up to each and every individual to decide how much those things apply to their unique circumstances, regardless of their orientations.