Daisy, The best bit of advice I had when I was a teenager who also thought everyone was looking me was this: think of 5 people you saw yesterday and describe their T-shirt or top. Can you do it? I couldn't and neither could most people. The Theory? No-one takes as much notice of the people around you as you may think. Everyone looks at people day to day. People avoid people unintentionally day to day. That's just what people do and how they behave. Most people can be looking at someone and thinking about what's for tea later, how they are going to pay such and such bill, or what time they have to pick up their kids from school, not everyone is looking at you and thinking about you.
Try smiling at people if they stare, they may not even realise they are doing it. Relax.