You don't need to test again. Your doctor sounds like he is not very educated on HIV. Oral sex is not a risk. You took a needless test and his recommendation for you to take another is a worry about his level of HIV knowledge as a physician. No risk, so no your result will not change. (and you don't need a test.)
You can breathe easy.
Here's the short answer on STI's for oral sex in general, and HIV in particular: oral sex is generally pretty safe - not 100% safe for STI's, but safe enough that you don't really need to worry about it. For a number of reasons, STI's just don't transmit easily that way. Among STI's, the one you're most likely to acquire through oral sex is gonorrhea, but, unless you're showing symptoms (discharge, pain during urination) within a few days, you don't have much to worry about. Other STI's (herpes, syphilis) can be transmitted by oral sex, but, unless you could see an obvious sore or lesion, you don't have much to worry about.
As for HIV transmission, there is some risk to the receptive partner (the person giving the blow job) if the insertive partner (the person receiving the blowjob) were HIV positive (about 1 in 2500). For the person receiving the blowjob, however, the odds are almost zero that you could have caught anything, even if the partner were HIV positive.
So, long answer short, sleep easy. You have no chance of catching HIV from this encounter.