Lightheaded, dizzy, blurred vision, HELP!?

I have been getting extremely bad headaches off and on for about 3-4 years. Recently, they've become more frequent and I've also been getting extremely lightheaded, dizzy, blurred vision, increased heartbeat, inability to stand on my own, feeling faint, and other symptoms like these. Anyone have any ideas of what could be wrong with me? I think I might not be getting enough sun, or maybe not enough calcium. I was thinking either vitamin D deficiency or I may be anemic. I've seen a doctor and they can't seem to figure it out either. Maybe it's just anxiety?! Who knows... Help :/