Hi Mr Gav,

Firstly i think u've to seek for physician(in internal medicien,neurology,orthopedic,) in order to give us more assessment about ur case..
Any way ,i think ur case seems like some one have an intermittent claudication(exercise pain due to cramping of muscles with exercises when there is ischamia,or being have a knee cyst (at the popliteal fossa),compression on fibular nerve,soreness wether from solues muscle or gastrocnemiuse muscle,

what about ur current gait,clinical history as being have diabeus milletus!!,...

hope his help u..

Regards