Hi . It is clear and understandable that you are troubled by these symptoms you are experiencing. You are correct that the risk from receiving oral sex is low. As noted in this article on transmission risk from our editorial team, the estimated risk from receptive oral sex is less that 0.04 percent: https://h-i-v.net/transmission-risks. Of course, this does not account for individual unique circumstances. It is true that the symptoms you mention may occur during seroconversion (see: https://h-i-v.net/symptoms/early-stage), but they can also have other causes.
Also, you mentioned 48 hours being in the window for potential seroconversion. The medical sites I'm familiar with mostly mention one to two weeks. This one from the CDC notes "These signs and symptoms of acute HIV infection can begin a few days after you are exposed to HIV and usually
last for about 14 days:" https://www.cdc.gov/hiv/pdf/prep_gl_patient_factsheet_acute_hiv_infection_english.pdf. This site specifically says "there are no symptoms of having acquired HIV only two days after a possible exposure:" https://www.thebody.com/article/can-you-get-hiv-symptoms-in-the-two-to-three-days-, but I need to stress that we are not medical professionals and cannot specifically confirm online medical information.
Of course, the only way to be sure is to get tested. All HIV tests have a window with a minimum amount of time before they can detect HIV. This article from our editorial team gives an overview of the different tests, with the window periods: https://h-i-v.net/test-types. We know that getting tested is hard, but it can also provide peace of mind. Also, if there is a positive result, the early treatment begins the better. HIV treatments have advanced dramatically and now full and happy lives are possible, as many here can attest. Wishing you the best and please feel free, if you like, to keep us posted on how you are doing and to ask questions. Best, Richard (Team Member)