Am very congested 3 weeks post-flu. have 5 nodes on each side of neck swollen (small marble size). is this normal? some are tender.

"Normal" is relative: in cases like this. It's "normal" for lymph nodes to be tender & swollen when they're trying to keep a localized infection from entering the blood stream. However, the underlying cause probably isn't "normal". Neither is it "normal" to have persistent symptoms 3 weeks after having the flu. Please seek medical attention. Dr. Anne.

Reactive lymph nodes: these are reactive lymph nodes due to your recent infection. They mean nothing and will shriink and become non tender over next 6 weeks. Nothing to worry about.