Are you circumcised or not? Yeast infections can happen quite easily under the foreskin because it develops in warm areas like the last poster mentioned. This might sound gross, but do the itchy parts smell? Particularly like bread? (I know, gross) Because this is a characteristic of a yeast infection (yeast's in bread, remember -- again, gross). If it does you can try a simple yeast infection cream (I know, super embarrassing to buy monastat or canesten cream but if it is a yeast infection it will clear it right up)...OR you could go to your doc and get an anti fungal oral medication.
It could also be a simple dermatitis or excema, honestly. Both can be treated with a cream. What type of laundry detergent/fabric softeners are used on your underwear? Excema and other dermatitis' can be caused from allergic reactions to perfumes and dyes in laundry soap/softeners. And of course if can also be caused by the soap or other body sprays/creams you are using.
HOpe this helps!
