On one hand not getting sick with the viruses is a blessing, on the other hand, people who never feel sick are statistically at slightly higher risk for cancer.
I kind of get a kick out of all the products to “build up the immune system”, if they were actually making the immune system more potent, they would cause more symptoms with the inevitable viral infections which we all get.
Based on your description, I would not be surprised in the least if you did have the flu.
That's a little disconcerting. :) Has anyone investigated why that might be?