Yeah I suck at my exposure apparently always under exposing.
How are you metering the images?
I would assume you are in an aperture priority mode and selecting an aperture to give the desired Depth of focus for the scene. The camera should then be selecting a shutter speed to achieve a good exposure. How the camera does this depends on what metering mode you use:
*) there is normally a matrix/scene/evaluative mode (terminology is camera dependent) that observes the entire scene and tries to make a smart choice balancing highlights and shadows. Sophisticated scene recognition is often done. Nikon cameras for example can detect things like blue sky, sunsets with the color matrix metering. This normally does a good job on all cameras but you have to realist it makes a balance so things like strong back lighting will cause an issue.
*) There is a center metering mode that is typically similar to the above but puts a much stronger emphasis only on the center of the images (the above matrix mode also favors the center but tries for a better balance).
*) I don't know about pentax cameras but every Nikon DSLR also has a spot metering mode. This is great for things like taking a photo of a person against a very dark or very bright background. The camera will meter under the autofocus point selected. Not all cameras have this mode.
If you use the matrix mode then you should be OK in most scenes. If you camera is always under exposing there might be a global setting that is forcing the underexposure. You will have to go through the menu options.
aAlso occasionally some 3rd part lenses dont work correctly with the camera and report the wrong aperture so the eposure is wrong.