I just wanted to share the following with you as it has worked wonders (so far) for me..
For the past few years my running has been curtailed by a rather annoying and increasingly painful left hip, to the point where I haven't ran seriously for at least a year.
Having been assessed on a recent course, I was found to have a significant leg-length difference of approx. 1cm.
So I fitted my right shoe (the right leg being the shorty) with a 6mm heel raise and off I went....in the past 5 days I have run a 7 mile off-road (1hr'15) and a 10k on-road (58:45) with no problems other than those expected for not having run for a year....slow as a cart horse and completely knackered-itis! Now I know it's very early days to be confident that my painful niggle won't rear its head at some point, but previously my running was limited to 45 mins before the pain took over.
Now, leg-length is a sticky issue in terms of accurately measuring it, any physio will tell you that. However, if you have any running related injury/niggle, then it's worth seeing if you can identify a leg-length difference. In standing, with your feet together and knees back, run your fingers up the middle of your thigh until you come upon a bony sticky-out bit (add appropriate comment as deemed fit), this is the front of your pelvis (ASIS). Using one finger per side, hook your finger under the bony bit and pull up to make sure you're in the right spot, you should feel the 'hardness' of the bone under your fingertip. Now look ahead into a mirror, are your fingers level, or is one higher than the other?
If you find one side is noticably higher than the other, then you MAY, have a leg-length difference (many variables can account for what appears to be a shorter leg length) which could be the cause of any niggles you have due to altered biomechanics as you're weight-bearing. The highest side would be the longer leg.
If you can't get hold of a heel raise then try using semi-compressed felt available from a cobblers, mark it around your heel, cut out and pop in your shorter side.
It's worth a try as its not going to kill you if you've put in a heel-raise in-appropriately (you'll soon know if its helping or not), but if it is indicated then you may just find it works a treat.
Obviously the ideal solution would be to see a Physio or other relevant professional.