Neck lymph nodes can be the result of tonsillitis, pharyngitis (infection of upper throat),
infection in mouth, caries in tooth, internal
ear infection, outer
ear infection, eczema, dermatitis, dandruff, breast cancer, fungal infection, other cancers like lymphoma etc. If you had flu like symptoms initially then it could be due to infectious mononucleosis too.
Please discuss this with your doctor. Take care!