Hi, The symptoms you are describing could be caused by several different conditions, so it is important to see a doctor for a proper evaluation and diagnosis. However, some possible causes of left-sided swelling and tightness in the neck muscles are: - Enlarged lymph nodes: Lymph nodes are a part of the immune system; they are small and bean-shaped structures. They can become enlarged in response to infections, inflammation, or cancer. If the lymph nodes in your neck are swollen, it could be a sign of an underlying condition. - Thyroid problems: The thyroid gland is located in the neck and produces hormones that regulate metabolism. If the thyroid gland is overactive or underactive, it can cause swelling or discomfort in the neck, as well as other symptoms such as weight changes, fatigue, and changes in heart rate. - Muscular problems: Strained or injured muscles in the neck can cause pain, stiffness, and tightness. This can be due to poor posture, repetitive movements, or physical trauma. - Nerve compression: If a nerve in the neck is compressed or pinched, it can cause pain, weakness, or numbness in the affected area. This can be due to a herniated disc, spinal stenosis, or other conditions that put pressure on the nerves in the neck. - Tumor or growth: In rare cases, a tumor or growth in the neck can cause swelling, pain, or other symptoms. It is important to see a doctor for an evaluation, as they may recommend imaging tests or other diagnostic tests to determine the underlying cause of your symptoms. Depending on the cause, treatment options may include medication, physical therapy, or surgery. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician