Shin pain/ thigh pain that disappears on exercise

Marked stiffness and pain in right leg when first straightening up after sitting, with sharp aching pain in shins.
Pain eases with exercise, but right leg feels stiff, weak and tired. Once the leg is warmed up, pain dissapears and can walk up to 12 miles climbing 3000ft, descending 3000 ft with no further pain.
At end of walk, right leg feels much more tired than left leg. Stiffness and pain returns rapidly on resting.
Overnight a lot of muscle twitching in right leg.
The following day left leg feels normal, ready for another days walking. Right leg still feels as tired as when ended the walk.
Doctor has done normal tests and can find no signs of joint or muscle problems, no pain on manipulation or obvious weakness. Not shin splints or compartment. No pain in knee.
Back is flexible and no tenderness anywhere.

Lying with left leg straight, crossing right shin over left shin and then moving the left leg to move crossing point towards left foot causes intense pain in right thigh and shin.
(No pain performing this action with left over right)

Previous history: Skiing accident 5 years ago landed heavily on right femur, and lost some mobility in right hip for almost a year. Full mobility recovered, and no restriction on hip mobility now.

1 year ago digging garden, developed sharp pain in hip/thigh after an hour using right foot to push in spade. Pain disappeared after a fortnight and has not returned – digging action has also been avoided.

Cannot stand around or walk slowly without developing sharp pains in lower back after about half an hour.

male aged 55, walks 12 miles over rough ground 2 or 3 times a week.

Any suggestions appreciated.