I have a swelling in the neck, but had no symptoms of infection or swelling in the groin or armpit. what should i do?

See a doctor: Swelling could be lymph nodes or thyroid, etc.

Neck swelling: Infection, inflammation, a tumor, or enlarged lymph node may all cause focal swelling even in the absence of any other symptoms. If this persists for more than 5 to 7 days, it is time to see your family physician or urgent care.

Yes: Lymph bodes can be enlarged and limited to one specific area. An exam would help identify possible causes.

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.