I have had left hip replaced but ihave a deep pain in butt with little bit of sciatica down to foot and also my 2 knees are burning and painfull?

Possible L5 radic. Your symptoms are at least in part consistent with a compression of the L5 nerve roots on both sides (right and left) with a bit more problem on the side that burns all the way to the foot. Neurological evaluation and possible EMG/NCV study recommended.