Why do i keep getting pimples in the same place!!?

i keep on getting pimples on my chin!! constantly... i occasionally get the odd one on my cheek or forehead...but they keep on popping up on my chin!!

why?

and how do i stop or prevent this!! please tel me becuase iv got disgustin pimple scars n it makes it look like ive been shaving my chin! ewww
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