Tenderness in the back left side of my head with neck pain and headaches on left side with no injuries?

Headache: Back left sided headache. Tension headache would be most likely. The insertion of your fronto-occipital muscle is in that area and that can tighten and hurt. Could be neck problem referring to that area or a greater occipital neuralgia. That is a nerve that runs behind your ear that can get irritated

Paracervical Strain?: It sound like you may be suffering from a paracervical muscle strain. I recommend trying moist heat, gentle neck massage and ibuprofen or naproxen. I would also purchase a cervical pillow. These may also be a sign of tension headaches, often due to stress, so include relaxation techniques. Seek medical attention if your symptoms persist or worsen. Take Care!