How Can Penis Shaft Irritation Be Treated?

Hi, I am a 43 yr old male, 5'8'' and almost 400 lbs. I have been having problems with skin irritation on the underside of my penis...I believe from left-over urine. I try to keep this area clean as much as possible. My penis tends to withdraw into the foreskin, so that when I have to urinate, I have to physically pull it back out. What can I do? What do you think is causing this? Is there an ointment that will soothe the affected area? Is it my overweight status that is causing this?
Louie