Is it std?

[Dan8923]

I noticed today that a portion of my penis has an unusual red color, I first thought it's irritated but it doesn't hurt at all.
A week ago I went to a prostitute, big mistake, she gave me about 15-20 minutes of unprotected oral sex and like 2 minutes of vaginal protected sex. Can it be std? If I go and run some blood tests will it show if I have it?
I'm only 18 so if it doesn't dissapear till tommorow I have to tell my parents, it will be awful X_X. Please give me some piece of advice.
Sorry for the possible grammar mistakes, I'm not a native and I'm really nervous right now.

Here is a picture, it's a bit more red in reality but that's how my camera got it.
http://oi60.tinypic.com/2qvfvyr.jpg

[Dan8923]

I see, but let's say that the redness is gone tommorow, does it mean it was just an irritation or should I still se a doctor?

[Vance2335]

I would get an exam before anything else.

[Dan8923]

Still, how long should I wait till I can get a blood test.

[Vance2335]

Skin issues can be many things often not a STD, but you would have to see a Dr.