There are 3 swollen lymph nodes on the left side of my neck and the doctor can't find a cause. What could it be?

Pursue it. Inflammatory response is a common response of ln with enlargement. A recent viral infection, skin eruption of head and neck area may be the cause. There are malignancies that may present with enlarged ln. Treatment may vary from watchful waiting, antibiotics, to needle biopsy of ln. Point is to have it followed by your doctor until it is resolved.
May need a biopsy. Swollen lymph nodes without a cause need to be investigated. There are many reasons lymph nodes can enlarge but it will likely require a biopsy to figure this out.
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.
Lymph nodes. Inflammatory, infection, malignancy. Do you have a young cat at home? Also, you should be seen by an oral surgeon to fully evaluate your mouth.

Related Questions

I have had swollen lymph nodes down the right side of my neck, should I consult a doctor?

No doubt. Lymphadenitis on one side of neck- can be related to oral cavity infection...Usually tender and accompanied by oral cavity discomfort. If none then it can be lymoma....Not a good dx. See pmd.

I have a few swollen lymph nodes in my neck. My doctor isn't concerned but I am b/c I keep getting more. If they are cancerous, will they grow?

Swollen lymph nodes. Yes if the lymph nodes are related to cancer they will grow granted at what time frame is hard to know. At your age, it is more likely that these are related to an infectious cause but lymphoma can also be of concern. If you are noticing hot flashes/night sweats or any other areas where your lymph nodes are swollen (armpits/groins), you need to share this with your physician.

It been a week my neck is sore underneath chin my doctor told me no swollen lymph nodes why can it be?

Gland. You may have a blockage of a gland that helps with saliva. One option for treat that is sialogogues (saliva inducers) such as sour balls. That may help expel a blocking stone. Consider also continuing md follow up to look at other possibilities if it doesn't improve.

I have had this lump in my neck all my life that fits the description of a swollen lymph node. The doctor says its harmless but swollen lymph nodes are only suppose to last like a few weeks and I've always had it. What should ido?

Some. Some lymph nodes are bigger than others, and if this has truly been stable throughout your life, then it's not something to worry about. Lumps in the neck aren't always lymph nodes. There can also be congenital cysts of various type that look and feel like a node but are actually just contained fluid. Again, the long-term stability of this in your case would argue pretty strongly against it being anything bad.
Not a lymph node. Lymph nodes swell when there is infection present somewhere in the vicinity. After the infection is cleared they will return to their normal size.
LN can stay big. Sometimes after a lymph node has enlarged due to an infection, it doesn't return to its previous size. I have two that got big when I had pneumonia over 20 years ago that I can still feel. I'd be more concerned if they were new and getting bigger, but if you've had them for years and they're the same size, they're probably nothing. If you're still worried, tell your doc.