The risks are very low for protected oral sex. Nothing you'd be at risk for would cause your symptoms.
Have you been checked for the flu, covid, etc?
The only things you might be at risk for with protected sex are genital herpes type 1 and syphilis. For giving oral sex, the biggest risk would be syphilis.
Syphilis is uncommon in most developed countries - the US, UK, Canada, countries in Europe, etc.
Work with your doctor to address your symptoms, but I'd be very surprised if it's because of an STI.