Help !!!

[Yash78]

Hey,
I am 18 Year old Indian Male. Until i was 15, i had very dense hair. But now whenever i see my hair under certain light, the frontal scalp can be seen. My hairline seems to be reciding. My left frontal are thinning.

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I went to doc, He said its normal. But still i am concerned. My father is 45 and have good hair. Please see the images attached and tell me whats happening...
Thanks...