Low back pain/twinge in upper glute

I have been experiencing a bit of discomfort the day after a particularly hard ride whether it be hill training or intervals on  the flats.    I feel a twinge in my upper glute (glute medius) and in the lower back just above this area.  Is my seat too far back?  Or is it too low or high?  Any general rule in regards to bike fit or body position when in the saddle?  It seems to be aggravated from hard pedaling while in the saddle.  Any input would be appreciated.  Thanks.

Your saddle could be set too hi, or your stem could be set too lo. Either way, you could be putting too much stress on your lower back. You should'nt be leaning too far forward when riding (like you see the pro's do).
Don't go crazee and adjust your seat or stem left, right and centre. Take it a few mm at a time, to give your body the time to adjust to the new position.
Do abdominal and back strengthening exercises aswell.

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Pain is inevitable...suffering is optional

I'm with VO2, I think your saddle is set too high.

To check get someone to stand behind you and look at your hips as you pedal.  They should be relativly level and should not rock up and down.  It might help to do this on a turbo and place a marker over your hip so its easy to see.