hello john.. welcome to healthcaremagic.. well you wont get infected if u sleep with a person once if the other person was not infected.. actually even if u sleep with many people you wont get infected as far as the person with whom you are sleeping is also hiv positive.. its just that if u sleep with more people the chances increases as you dont know the hiv status of other people.. and when you have intercourse using protection like condoms there wil be very least chances that you acquire hiv.. so use condoms.. the symptoms which you are having like fever sorethroat and headache are nonspecific and those symptoms may be seen in lots of diseases.. so nothing to worry about it.. there are hundreds of symptoms seen in hiv so u cant just tell that they may be due to that.. infact you may be having sinusitis and sorethroat for which you should get consulted if severe.. and i think its worthwhile to get an hiv test done once again.. and do use condoms next time.. i hope this solves your query.. thanks & take care..