Question about tip of penis

Strange spot on tip of penis (or I think as I have never really examined my penis). Four doctors have told me it is absolutely nothing and in past 4 weeks had two full sti panels, and everything came back negative. The doctors all told me it is not Hpv. I have generalized anxiety so I was told but all doctors that because of my anxiety disorder I'm just making matters worse by over thinking about it. Any help would be appreciated of what it could be.

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