How To Get Rid Of Dark Neck?

hai,i'm 17 years old girl.my problem is,i noticed that my neck is very dark.maybe it is not because of my real skin colour,but i guess it is because i used to play very often under sunlight and i rarely take a shower after that because u know,im still a kid that time.my sister used to told me to scrub my neck after playing,but i just abandoned her advise.an now,its already almost 7 years and my neck do have dirt that was already 'become' my skin colour.its awful and very ugly.i've tried many product but none of its working.i'm ashamed.btw,im quite an overweight person,is that one of the factor 2?tq doc!