What Causes Dizziness And Headaches?

I have been getting light headed for quite a while year maybe more. When i stand my legs get weak i have to grab onto something or I will fall or faint.My eyes have so much pressure i have to keep them closed until it passes I see black and white flashes. I shake as if i am fainting but i am consious and it passes. I get head aches all the time at least 4 days of each week. It comes and goes all the time some days are worse then others any helpful thoughts would be great I cant afford to go to a doctor so i appreciate any advice. Thanks Jessica