Guys are usually very defensive when you tell them to use a condom; they'll make a million and one excuses NOT to wear one, but then they get some sort of infection they usually say "Gee, I wish I would have used a condom."

Anyways, retract your foreskin and wash under it with warm, (running!) soapy water twice a day. Pat it dry, and let air get to it whenever possible. If you have any 3% hydrogen peroxide, try using that before you get in the shower; it'll kill the yeast/bacteria that's causing the irritation.