Hi
1. we dont use what ifs here but only what real and oral sex is zero risk for hiv. To address your answer as your stating it would only enhance your anxiety.
2. When it comes to flu symptoms in the realm of std,s we would be referring to herpes and with herpes a blister sore would appear before the flu like symptoms. No blister you can pretty much rule out herpes.
3. If you have a long term partner then you would be putting them a risk for herpes, syphilis and NGU from oral sex so it would be advised to test for these before being intimate them. Even low risk is not fair.