If you are worried you should go for a test, but nausea isn't a recognised symptom and in any case probably isn't related to the sore throat if the sore throat occurred 5 days later. Sore throat would be immune reaction to a virus inhaled, or could be sexual activity if you had oral sex. However the sore throat would normally happen before five days so is more likely to be reaction to an airborne virus. On balance I think you are worrying unnecessarily, but go for the test anyway, you may have to wait though. It's only after 6 months you can be sure a negative really is a negative.