My head feels heavy and lightheaded?

I went to the doctors and they said my vitals and everything are good: no diabetes, no thyroid problems, nothing wrong with my heart, kidneys and everything is all right. So what could be causing my lightheadedness I wonder? I feel a little foggy in my head, like something is putting pressure on it and the back of my neck feels like it’s having pressure on it as well. What could be cause? And I would extremely appreciate if anyone could give a good answers! Thanks to all who answers!