Penis Irritation after sex

I'm a 23 year old male who has had 3 sexual partners in the last year. Some sex has been protected, some hasn't. A while back, not sure exactly when, but at least 6 months ago, a spot began to develop on my penis after I would have sex with my girlfriend, regardless of whether we used protection. The spot was usually a red raw area, circular in shape, flat, not raised. It does not ooze pus, and is not a growth of any sort, as far as I can tell. The spot would usually scab over just like the skin had been rubbed off anywhere else on my body and then heal within a few days and fade, but not completely disappear. Each time I had sex, however, it would reappear in the same place. Additionally, when I masturbated, it would also show up (but would not be raw because there was considerably less friction when I masturbated) and would be very light. I can tell during sex that the spot is developing because it becomes raw, as if from friction. I rarely if ever use lubricant, even though I know I should.

I have had sex with two girls since breaking up with that girlfriend, and each time the irritation returns in the same spot. The irritation also returns if I masturbate more than a couple of times a day.

While I hope that this is irritation, I am concerned that this is an STD like Herpes, because I know herpes spots scab over as well. I purchased some Hydrocortisone cream today and started using it to see if the spot would clear up.

Any opinions on this? I am going to get an STD test on Friday..but I am looking for some early opinions on what it might be.