I used to have have horrid hip pain when I walked any distances, I have discovered (that sounds easy) that my deep hip flexors are very tight whilst my gluteals just don't fire up at all. It really felt like something was being jabbed into the front of the groin. I am slowly getting better with the help of a lovely private osteopath, NHS physio, and Pilates. Everyone is different of course but I have found that some good hip flexor stretches combined with isolating and building up the gluteals has really helped. It has also taken the pressure off my lumbar back, though I still have to be very conscious and deliberate with every movement This has all been prescribed to me by professionals so please get yourself checked out properly before you try anything.
I have another theory about my own walking and this sounds like it might apply to you too as you only get the pain when you do 'determined' walking rather than the type of walking you do when you are shopping. I was the youngest of four children by five years and my older siblings and father were all very tall, I had to learn to walk very fast to keep up so developed a very long stride which no doubt overextended my knees and hips, I now try and consciously keep my strides a little shorter and don't 'flick' my knees out at the end of the stride. Hope this helps.
migraines, fatigue, multiple chemical sensitivities, gluten and lactose intolerance, bursitis, ulna nerve pain, hypermobility, and possibly POTS.
Finally Diagnosed with HMS/EDS on 5th September 2012 by Professor Grahame