Why do I experience pain when the tip is simulated?

By tip I'm sure you all know what I mean. but when it's stimulated at all its like it's too sensitive and it creates this intense sharp pain at the tip that so painful and unbearable I hold my breath and try not to yell cause it hurts that bad. The shaft is fine, but the tip feels too sensitive.
Why do I experience pain when the tip is simulated?
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