I had protected sex with a girl (i wore a condom), and around a month later i noticed a sore (about half the size of a dime) under the bottom of the head of my penis. I didn't notice any signs or the sore itself until after being with my now girlfriend and after she had been repeatedly stroking my penis. [I have gotten a sore place on my penis before from masturbating too hard or much but even before having sex for the first time. -as if from rubbing skin off due to the friction] The next night she started rubbing it again, and it stung a little bit. I noticed that she had been wearing a ring on her finger and thought that could be a possible reason for the sore. ..either she had scratched me with it, or that it had caused the sore by rubbing up n down against the skin. the sore only was there for about a week. I've only had sex a few times in my life, and everytime I have used protection. However, within the last month I haven't been getting erections quite as frequently and easily, and I have been feeling sick the last couple days. [note i do smoke so this can contribute in some aspects im aware] I know there is the possiblity of coincidence, but does it sound like i might have an std?