Why do I feel lwk like a fraud?

Like (i think) im trans, I feel euphoria from clothes, shaving (although the good feeling might be coming from just self maintenance), etc. I feel like id be happier with a more feminine body, (sometimes) I get a bit disappointed when i look at the mirror, or just my general build, but i cant just shake the feeling of pretending, faking, or some other factor being the cause to this or it just not being enough to say im trans. Is there any way to with near complete certainty, figure out if your trans? Also, how do you shake the feeling of shame?