activity, a fungal infection or dermatitis is a likely differential here. Balanitis may be a likely diagnosis for your case. Balanitis is a skin condition affecting the head of the penis. The risk for balanitis increases when one is uncircumcised. Balanitis may include fungal infections and dermatitis.
In your case, wash the area with a mild cleanser especially after urination. Keep the area clean always. Avoid using lotions or creams unless prescribed by your physician. At this point, you may apply 1% hydrocortisone cream thinly over the affected area once daily for 3 days. See if this improves. Do not use for more than 1 week. If symptoms persists, then you may need further consult.