I'm sorry to hear school isn't going well for you...that's really tough.
When I was in high school, I carried a bean bag dolphin in my purse....I never took her out, but the knowledge that she was in there and close by was reassuring. She was just my friend. These days I carry a small Tsum Tsum plush in my pocket, along with some other stim toys/objects like a Tangle toy or a worry stone. If you have a bag or backpack that your doll can travel in alongside you, or is small enough to fit inside a pocket, that might be the way to go. No one has to know your doll is there, then.
That being said, I'm certainly not trying to say that your wanting to bring your doll to school is "wrong" or "unusual" at all - on the contrary, I completely understand your need for that kind of companionship that dolls (and stuffed animals, toys, etc) can give when it is not forthcoming from other people. It's totally fine, and anyone at your school who gives you any sort of trouble over it should be ashamed of themselves. I still have residual emotional scars from when my stepfather found out I'd taken a small plushie of Stuart Little to school in 3rd grade and punished me by locking him in the car's glove compartment overnight. All these years later, I'm still not sure what he hoped to accomplish with that....such an action is more to be expected from your typical school bully or mean older sibling, not a parental figure. Anyway.....
I hope things get better for you as far as school is concerned (and just better in general), and that you're able to bring your doll with you to school w/out a problem, if that's what helps you feel more comfortable.