What if you have open sores on your penis and your partner hasnt had sexually intercourse with noone else , then what can it be?

STD: The highest likelihood for any sores on the penis is stds, period. You should go get evaluated and screened by your doctor. However, that doesn't mean stds are the only cause. There is a rare autoimmune disorder called behcet's disease that can cause genital ulcers (among other things); however, i wouldn't just assume this without a proper evaluation and screen for stds.

Probable STD: Have you had prior intercourse. See your doctor when they are opened. Have protected sex until you find out.