Skin pigmentation on my genitals

I am a 27 year old male. Since having sex with my new partner exactly 1 year ago, a large patch of skin under my penis shaft has become white in colour, and become itchy, and blotchy patches of white have arisen around other parts of my genitals.

I wondered if there was a cream to stop the spread of this, and whether I should consult my local doctors surgery.

Many Thanks