What Would Cause Lesions On A Penis?

Hi after noticing that my trousers and underwear were irritating the head of my penis (circumcised about 6 yrs ago) I checked it out and there appears to be a single small reddish lesion on the glans that stings when i put pressure on it. Happened overnight apparently. No other symptoms and I haven't slept with anyone for over a year. Am a little worried. Any ideas?