For so many years I had this very small bump on the back of my neck it feels like a pimple almost but it's under the skin. Has not changed.?

Stable skin lesion . Bumps under or within the skin have various causes. The most common are dermal nevus and cyst. In general, lesions that are unchanged for years are harmless. Be more concerned if the bump enlarges, crusts or bleeds. Diagnosis is often easy for a trained doctor but sometimes the lesion has to be surgically removed as a precaution.
Bump under skin. Painless lumps just under the skin are likely cysts. They can gradually enlarge with time. If you have concerns about it then have you doctor confirm the diagnosis. Sometime cysts are removed to relieve symptoms.