I try to texture, and even when I paint the full unwrapped image there’s absolutely nothing EXCEPT for one singular block painted. Please help me because I have no idea what to do
I notice (from the image that you posted) that you have the Viewport Shading set to Solid.
To see texture painting on an object you will need to:
-
add a Material to object to be painted, that includes an Image_Texture node. The Image_Texture node will need to reference the 2D image where you are storing the pixels (.PNG or .JPG …).
…Whether you go find an image outside of blender, or hit the [+ New] button to generate a blank image inside blender: in the Image_Editor (flat 2D version of image) you will need to go to the menu “Image” to Save changes (the menu name will changed to “Image*” (with asterix) to warn you of unsaved changes). -
have Viewport_Shading (little buttons in header of Viewport in the extreme top-right set to either Material_Preview or Rendered (the 2 buttons to the more right of this set of 4 Viewport_Shading buttons with little circles in them).
testing this, I see that my step ‘2’ is sometimes not required in Texture_Paint mode, but when you switch back to Object or Edit more, it IS required.
switching between workspaces and then back to Texture_Paint workspace, it seems that step ‘2’ IS required the 2nd time in (change Viewport shading to Material_Preview or Rendered).
If you are using an external image file, sometimes it may get lost or separated from the blender file. Look for the option to “Pack” image into the blend file. This will increase the size of your blend file (by the size of the image), but now they can’t accidentally get separated.
I hope some of this helps. 
Aren’t there multiple materials applied? Only a part of the material is visible.
Check out the material list. 