Well, to be positive, whether it is 7 sec of unprotected sex or 7 mts it doesnt matter much.. Its just yes or no.
Hiv transmission in an single encounter of unprotected sex is 1 in 300 to 10,000 as per medical documents. But that can surely not encourage one. The only way to be sure is to get tested.
Though weight loss is one of the symptoms of a early acute infection happening during the window period, it is not consistant symptom. As you said, it can also happen due to stress and anxiety.
Good that you took the first step to get tested. Test again after 3 months to get confirmed.
Oral sex has some effect on transmission, though low. Female to male transmission is lower than a male to female transmission. Female to male transmission is more positive when the female has more blood flow and that happens to get in touch with the male body.
More than that, protect yourself in the future. Do not go for unprotected sex.