Hip pain following spinal fusion

I have had a spinal fusion on 4 levels which was done in 2 stages.  First stage the surgeon went into my spine sideways and replaced 2 discs with cages and then 2 weeks later went through my back and put another cage, 2 plates and 8 screws.  I am pleased to say that I no longer have lower back pain but I can only stand and walk for short periods of time as my back tightens up and I get pain in what seems to be my right hip.  Has anyone had similar and do they know what it is?