Why are people so bothered by my face?

I have a visible birthmark on my face that has the shape of a beauty mark on my cheek. I always cover it with makeup but it never fully gets concealed so the result is like a skin-colored spot on my cheek. However, people always focus on it and give me weird looks, which makes me self-conscious and makes me wonder if I look way worse than I thought. I wish I could just say that people never care about that stuff as much as I do, but it’s false in my case. There’s even this girl in one of my classes last semester who would always look at my birthmark while speaking to me and she would squint her eyes every time. She even made a disgusted face once while looking at it. And she would go as far as to look at me during exams (while she got up to ask a question to the teacher) and her eyes were fixated on that specific spot on my cheek. I understand that people might get curious or intrigued but these reactions make me feel like I’m just disgusting for looking “different”. And it’s not only a one time thing, it happens very often. I sound like I’m going crazy but it’s genuinely exhausting and my insecurity is starting to take over my life. How do I change things?