Allergic reactions can be a cause for swollen lymph nodes same as bacteria and viruses.
Also, children and young adult tend to have a more active lymphatic system, so their glands may feel enlarged.
Abnormal size of lymph nodes are size bigger than 1 cm for neck lymph nodes and size bigger than 1.5 cm for groin lymph nodes, but, still some doctors accept the range 1-2 cm like normal.
Do you suffer from arthritis, thyroid gland disorders or metabolic disease?