Like the doctor says, "If it hurts when you push on it, STOP pushing on it!" Leave your neck alone! That is the ONLY reason it's sore.
Do I understand you correctly that the sexual encounter you are so worried about now was NOT with your girlfriend? That's very gentlemanly of you not to want to "hurt her in any way," apparently sleeping around behind her back wouldn't hurt her if she found out? You also say that you think you should stop having sex until you get to know a girl well, and to get tested before you "do it" again. Don't you know your girlfriend very well? She's been tested twice and you've been tested SIX times!?
Did you go to the HIV Anxiety Forum I gave you the link to? Here it is again.
http://www.medhelp.org/forums/HIV-Anxiety-Support/show/595
You need to get into some therapy for your HIV anxiety, which is out of control. Getting yourself educated about HIV/AIDS would be a good way to spend your time while you wait for your therapy appoints to begin.
Since you need to wait until February to get tested, I would suggest not having sex with your girlfriend either. Even if you always have protected sex, why would you be any safer with her than your "bit of stuff" on the side? Maybe SHE plays the field too. Do you know HER well enough to trust her? YOU obviously can't be trusted..............
Get some help
Greenlydia