cheesycow5,
a juice fast or feast is unlikely to be effective against infection in comparison to a water-only-fast, and where the most common cause of swollen lymph nodes is infection.
If the swelling appeared suddenly and is painful, it is usually caused by injury or an infection; but enlargement that comes on gradually and painlessly may, in some cases, result from cancer or a tumor.
You are best to have it diagnosed professionally, whilst simultaneously conducting a water-only-fast which will eliminate the problem thru autolysis.