Hi there -
It could be the flu. Really.
HIV is almost never passed via oral sex, so that's not a concern. If you are concerned about having an std or HIV, why not go to a GUM clinic and just test? That way you can stop speculating, and either move on or treat what you do have, if you have anything.
If your gf has ever been with anyone else, she should also test.
Aj
*sorry fly should be flu.. also that was my first time anything related sexually.. also she only ever had sex once. both 23.. live in the western world.. england to be exact. just knowing what fly like symptons can mean.. HIV. new to the forum.. fantastic idea.. cheers