Unprotected oral sex is much lower risk for all STDs than vaginal or anal intercourse, and probably zero risk for many of them. The main recognized risks of fellatio (i.e., for the insertive partner whose penis is exposed) are gonorrhea, herpes due to HSV-1, nonchlamydial nongonococcal urethritis (NGU), and syphilis.
Gonorrhea virtually always causes symptoms; if within a week there is no abnormal penile discharge, usually with painful urination, you can forget gonorrhea. Herpes risk depends in part on prior infection; as you say, it is not a risk in people with prior HSV-1 infection (or low enough to be disregarded). The frequency of NGU isn't certain, but if you have no discharge or uncomfortable urination after 2-3 weeks, you can disregard it. (In any case, NGU due to oral bacteria may carry no health risk for a person's other sex partners.) Syphilis is uncommon after oral sex, but the risk depends a lot on geography, partners' risk factors, etc. Syphilis usually shows up as a painless penile sore (the chancre) 3-6 weeks after exposure.
Everybody worries about HIV, but the risk is theoretical more than real. Although there have been claims of acquring HIV, there are few if any proved cases. If it occurs, it is extremely rare (estimated at no more than 1 chance in 10-20,000 exposures to an infected partner). Still, the wise person in your situation will ask a male partners whether or not he has been tested recently and whether he has HIV.
So the answers are that your GF probably isn't in danger, the risk you are infected is minimal (assuming you still have no symptoms), and most experts would not have prescribed the antibiotics--but if you take them, you're pretty well covered against the bacterial STDs.
HHH, MD
So by taking the oral antibiotics and only engaging in protected sex with my GF until finishing the medication my GF should definitely (obviously can't guarantee it but in all likely hood) be ok.