I Have Been Getting Very Faint Like When I Stand

I have been getting very faint like when I stand up. I have to hold on to something and wait a few minutes for it to pass. My scalp on my left side of my hair is very tender and sore for several weeks now. I have had a few headaches some, but not everyday. When I am trying to have a bowel movement and I am pushing I also get that faint feeling and I have to put my head down until it passes.