I too was and still sometimes am in the same boat. I am 21 right now, and growing up I was the rebel when it came to fashion. I wore a lot of black, dyed my hair wild colors and listened to loud music while the "princesses" had daddy's money to spend on expensive things that I wouldn't personally buy if it was on sale. I was the "cool" girl, the ferocious friend, but never considered beautiful. I had curvy hips though I was skinny and a nice round butt. At the time, girls my age picked on me, but as we got older, those same skinny minnies as my mom called them were envious of me because I had grown into my shape. I was the epitome of what they couldn't be: unique and fearless. I met my husband when I was 16, and he was a little older. He loved that while I was beautiful, I wasn't a carbon copy. And he was an "a**" man lol. While I may not be model beautiful, let's look at what is considered beautiful by those standards: unhealthily thin, no hips, no but, and let's be honest, a lot of those girls aren't very pretty. My husband seems to think I have a timeless beauty that will get better with age. I don't have a face that is easy to get confused with others. Now I am maturing in my fashion, and it's still me. I have tattoos and jet black hair, annd it looks good on me. The preppy look wouldn't look right on me and I'm more than okay with that.
Now this pertains to you as well because scars that deep especially when incurred that young stick with you. Buying new clothes and makeup won't help your feelings unless however you're dressing in a way that others want instead of how you want. Those insecurities can be nagging, but sometimes the best thing to do is figure out who is really thinking them? You or those kids at school. Kids are cruel and say things when they're jealous. Kids are also stupid at times. (honestly who puts their status on how much they paid for a pair of jeans?) If the insecurities keep coming, a therapist may be in order. A good one that's willing to talk to you, not one that just throws meds at you when you walk in the door. That said, sometimes, as in my case, medications may be needed for depression or OCD. That can severely affect your outlook and there's nothing wrong with taking them if you have to.
Finally, look at who you are now. Who DOES like the way they looked as a kid

I was a chubby little thing, but it grew me into who I am now. Also, did those rude comments fuel you to better yourself? In my case, I usually had to keep to myself and it made me work on my creativity, and I am now a Jack of all trades when it comes to art, including drawing, painting, sewing, and cosmetology, all self taught. It also let me see how little the opinions of those kind of people actually mean, and it made me a fierce advocate for myself and in turn my friends. I realize it turns some people down the wrong path and bullying is never a good thing, but before I was shy and didn't say a thing when people were cruel to me... until I had enough. In a way, it did me good. See if you can find any good in what happened and if it can bring you any solace. I wish you the best of luck!