I seem to have a lymph node on the side of my neck that increases and decreases in size from month to month. is this worth a trip to the doc?

Possibly: If you are troubleb by a single lymph node, that cyclically varies in size, this may be related to - for example - sores or a small scab on the face of scalp, or sme mild reactive process. Worst case scenario would consider lymphoma, but in such instance, ordinarily more than 1 node is involved, and there is no real cyclic activity. If the node is problematic to you, consider going to the doc.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.