I feel tension constantly behind my eyes as if someone has pulled my optic nerves taught. And there is a faint big black spot in my central vision?

Eye visit. Any fixed black spot in your central vision that does not resolve indicates an eye problem requiring prompt examination. With eye pain, could have some kind of optic neuritis, otherwise could have some retinal disorder.
See an eye doctor. The symptoms you are describing should be evaluated by an eye doctor. This can be caused by a serious condition that needs prompt attention.