Reddit mentions of The Fast Metabolism Diet Cookbook: Eat Even More Food and Lose Even More Weight

You sound very intelligent for someone still in high school. That will get you far, though the only downside to intelligence is the tendency to overthink. It's a blessing and a curse (mostly a blessing, though)

You sound like you have a clear idea of what your goals are, but just need some help getting there.

Definitely getting into shape will do a wonder for your confidence and physical wellbeing. I'm 25, and have struggled with my weight since I hit puberty, but I think I've finally found some light coming through the end of the tunnel after tons of research about weight loss. As it turns out, 95% of weight loss advice floating around on the internet is false, and the reason it varies so much is because there's an actual science behind it and not a one-size-fits-all approach. If you've tried losing weight before, you probably have my body type (endomorph)

This is the book that's changing my life currently. I'm sure it's available for a cheaper price used. If you can buy it somehow, I seriously recommend that you do. You might not be able to implement everything that's in there yet since you probably have no control over what foods get brought into your home, but knowing the science behind weight loss is very powerful knowledge. I wish this book existed when I was in high school. Because being overweight is not only a confidence shrinker, it'll eventually lead to a ton of other health problems (to which I'm only 25 and am now experiencing unfortunately, had to drop out of college temporarily because of it) Once you learn the scientific way to keep weight off like I did, it should be a very exciting revelation. (I actually cried after reading the first few chapters)

As for Obsessive Compulsive Disorder, if it's disrupting your daily/nightly life, getting help for it would be a good idea. If there's a chance that the way you approach your mother will get you to recieve help, I'd say go for it and try to get it.

I have OCD, but it's not severe enough to have clinically gotten diagnosed. I figured out how to stop doing as many rituals that were disrupting my life (at one point I injured myself pretty severely from a nightly 45 minute ritual. That's when I knew I needed to either seek help or learn to curb my symptoms somehow) I had mild facial tourette's as well (I still have it sometimes when I'm stressed) I started curbing my super long and detrimental rituals by replacing them with less invasive rituals little by little, until they became a lot shorter and less physically demanding. The dangerous stretching ritual I was doing before bed slowly turned into posing, then the posing became less frequent, so I was still satisfying tbe compulsion, but modifying it slightly each time. Exercise also helps with this for some reason.

I didn't have a sister that used to sort of steal my friends away from me, but my childhood best friend used to do that, since she was much more outgoing and comical than I was. I had to eventually let her go, which was a very hard decision to make, but ultimately when we stopped being friends, I was finally able to make my own friends (also as a side note, if you love music, concerts are an amazing place to make friends. My high school also had over 1,500 students - plenty of people to chose from, so she couldn't steal all of them away if she didn't even know who they were. But, since the person doing this to you is your sister, this might not be applicable for you until you're out of the house and/or in college (to which hopefully you chose one different than your sister's)

It sounds like you're past the point of trying to talk to your sister to tell her how you feel, but if you haven't tried that yet, maybe it would actually be helpful. Some people have no idea that they're hurting you until you tell them. If I had the verbal skills in high school to tell my childhood bestfriend how I was feeling, maybe we wouldn't have had to stop being friends.

Hopefully some of this helps you in some way. A lot of what you said reminded me of myself when I was in high school, minus the family dynamic.
I wish you the best.