How can I make my mom understand I hate how I look? ?

sad..... change your look as you want

Bet you're cute now, why change what isn't broken is probably what she's thinking.

while under her roof u need to obey her rules. when u move out you can do what u want. Although i do think u should be able to get a hair cut.

been there, done that. i was disobedient as hell when I was 17 (22 now). I cut my hair after my mom refused to let me, pieced my own ears and nose, all that. looking back, I don’t regret it at all, but wish I was more respectful to her.

Talk to your mom and let her know how you feel. You’re almost 18, and you’re about to reach an age where you should be able to do what you want..

BUT, 

You’re under her house and her rules. Maybe opt for alternatives (temporary hair dye, fake jewelry (there are hella cute fake nose rings and cartilage piercings online). As far as makeup, you are grown enough to wear it. Carry a makeup bag with you on your way out to wherever (school maybe), put it on, and take it off right before you walk into the house. 

How can you possibly "feel like yourself" if you effectively need to be in disguise to do it!

If you cannot accept your appearance as you naturally are, you will end up with mental problems or psychosis.

It may not seem like it now, but she is doing you a favour.

All the people I knew from school a few decades ago, who used makeup daily  wrecked their skin and now wear it like a mask.

They dare not live without it now, as they need to hide the damage they have done to their skin.

The people than never or very rarely used it look half the age of those.

The only people it benefits are the manufacturers; it's a kind of addiction.

while under her roof u need to obey her rules. when u move out you can do what u want. Although i do think u should be able to get a hair cut.