What Causes Red Spots On Penis?

hi, I woke up last week with a little red dot on my penis. Its really small and don't hurt or sting. I've been getting more of this small dots, they don't hurt they are not close to each other but I am worried. I am very care full on my sex life and always use protection. But two month ago i did have unprotected sex with my ex girlfriend and well this has me thinking if its an std or something else.