Why do people always stare at me?

I'm a 21-year-old female, and I experience some anxiety when I'm out in public, largely due to being badly bullied in middle school. I often notice people staring at me when I'm doing homework or walking around, and it makes me uncomfortable. I understand that people might not mean anything by it, but it still heightens my anxiety. I'm working on managing this, but does anyone have any tips for calming down in public?