Girls, Why do girls laugh at me?

Anonymous
So today there was a group of 4 girls from my school. I 've never seen them again, they were heading for their class while I was going to mine. I look at them. They saw me, So I looked away. After about an hour I saw them outside the building I walked by them they were talking, and when I passed by they giggle. I was chatting on messenger when I passed by so I didn't look at them. This thing happens to me every once in a month and it's always strangers. But I also caught some girls staring at me when I go downtown. They mostly talking to each other while they take a glance of me when I look at them they usually look away and then they mostly look back when I look away. I consider myself as a pretty guy not hot , neither ugly nor average sth between average and beautiful. So why they keep doin that? I don't have that much of self esteem.
Updates
+1 y
Well they laugh but when I move a bit further they stop
Girls, Why do girls laugh at me?
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