This could be many things.
Lets begin with the most simple solutions and work toward more complex ones:
1) Check your exposure compensation. Is this setting +? If so, change it so that it is no longer + or -.
To change exposure compensation, simply press the (+/-) button on the top of the camera near to the shutter release button. Then, roll the thumb wheel left or right until the reading is neither positive nor negative.
2) The K-70 has several metering modes for measuring the light in a photograph. Adjust your metering mode to 'Matrix' Metering.
If you are unsure how to do so, watch the following video.
3) Inspect the blades of your telephoto lens for oil.
If oil is present, the lens' aperture will not close down very well due to increased friction. This results in overexposed photographs.
To check for oil, simply remove the lens from the camera, set the aperture ring to the A position (or ~f/22) and close the bayonet on the back of you lens with your finger. Look at the aperture blades through the front of the lens and then the back of the lens. If oil is present, you can get your lens repaired at VanCam in Vancouver BC for ~$100 Canadian. They do good work.
UncleVanya and AstroDave give good advice! Try their suggestions too.