HIV risk level and symptoms

Doctors,

I am a 27 year old heterosexual man in NYC, and I have been having casual sex with a girl over the past few months.  There were a few times (about 5), after nights of drinking where we engaged in unprotected vaginal sex; the last time being three weeks ago.  

This past week I came down with flu like symptoms for two days, and actually went to the doctor.  He said it was a flu and prescribed Tamiflu.  Since that time, I am feeling much better, but I am a little concerned that it could be the early symptoms of HIV for a few reasons.  

First, for the past couple of weeks, even before the flu like symptoms I have been getting a recurring canker sore in the same spot on the bottom of my tongue.  Additionally, I have a rash on my hands that has been there for the past week and a half or so.  It is a cluster of small red bumps that itch on both hands; they are on the side of my hands and wrists, as well as the knuckles and the backs of my fingers.

I asked the girl if she has any STD's or HIV and she said no; but she admitted that she has been sleeping with other men.  I can only assume that some of those encounters were also unprotected.

Can you tell me how concerned I should be?  I know I put myself at risk, but to what degree?  Are the symptoms I described and the timing a greater cause for concern?  I know you say that there is no need to test after every sexual encounter, does that hold true in this case?

Thanks for the help.