What could cause lymphnodes in both sides of neck to swell? and what other tests are done to check for swelling of other lymphs in body? swollen 3 yea

Monitoring Centers: The lymphatic system absorbs/carries things too big to go into arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph to see if anything bad is there like bacteria, viruses, cancers, etc. When it detects a problem, it alerts the immune system and they enlarge in response to inflammation when they react. If no problem, they shrink. Biopsy for concerns.