I understand your concern. The rash you describe is compatible with the rash of the ARS HOWEVER, please remember that there are no well documented cases of HIV transmission by oral sex, that you do not know that your partner had HIV, and that the ARS is typically not an isolated rash but is accompanied by flu-like symptoms which include fever, muscle aches, etc. Thus is remains much, much more likely that your rash was due to something else (acne as you suggest, some other community acquired virus, soap or other chemical exposure, etc). If it was ARS (which is most unlikely) now, almost two weeks after the appearance of the rash, your HIV test would be expected to be positive. if you chose to get tested at this time and your test is negative as I suspect it will be, you can be confident that you did not get HIV from your exposure.
The odds are VERY MUCH in your favor that you are not the first person to get HIV from oral sex. Hope this helps. EWH
Thanks again