Left lymph node in neck swollen & marble size, and only left side of throat really sore. Some sort of infection?

Most likely. Most likely lymphadenitis which is an infection of a swollen lymph node. Could also be an infected cyst as well as a few other things.

Related Questions

Have small lump behind my r ear. Painful & lymph nodes in r neck swollen making neck hurt on the r. No other symptoms of infection. What is it? Er worthy?

See PCP. It is important to check out multiple lymph nodes enlargement in the neck. It is better to see your pcp so that proper exam, investigations and follow up can be done. Er is for acute illness only. Read more...
Not ER worthy. Sometimes lymph nodes can do this. If these don't resolve or if they spread you should see your doc. Read more...
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. Read more...

How to tell when a lump in the neck is a swollen lymph node or something else? My lump is not sore either. On left side only!

Get examined. I believe these are reactive or benign reactions to your previous story of runny nose but since it is low on neck and on left, have a clinic doc examine that for you. The definite way to tell noninvasively is by radiologic imaging or even a biopsy But those procedures are only planned if your clinic doc saw your person, evaluated your lump and decides. We can not tell by just reading your notes. Read more...