You cannot get STDs from physical contact that you described. Plus, symptoms of most STDs take much longer to show up. It is possible that it is mono, in which case, I don't think you have anything to worry about because rarely is it fatal. It is a self-limited illness which will go away by itself.
In any event, you are going to the doctor and he/she will be able to give you a more accurate diagnosis as I am not a doctor.
It sounds like your fatigue could be stress related. I'm not a physician or anything, but if your fatigue continues... you may want to consider seeing your physician.
I believe the fatigue could be. She was not my wife. Never did anything like it before and will not again.
I've just felt kind of like I'm fighting an infection, kind of tired and washed out. Did not know if Mono could develop that quickly to show signs that soon?
Could be some other unrealted infection I guess.
Do you think that your symptoms could be due to anxiety... due to guilt over cheating on your wife ? (I'm assuming this girl wasn't your wife)