Welcome to healthcare magic!
The joint replacement
very frequently results in stiffness
of the joint due to scar of healing.
Pain may be due to graft loosening or graft failure, infection, dislocation to name a few.
At the time of surgery there is signicant tissue handling by incision and cautery, the intervening nerves also get damaged.
Your hip pain seems to be related to a stiff joint and probably you are not walking with a balanced gait that means one side is over burdened and gets fatigued and starts aching, another possibility is neuropathic pain
of nerve damage
I think you should try local hot water bottle compresses to soothen it and a good physiotherapy
Include regular walking in habit and maintain straight posture, if needed take walker- but please have a walk daily.
If that does not help then you should get investigated by your operating surgeon.
I hope this advise would be helpful for you.
Still if you have any queries or doubts, please write me back,
I would be happy to solve them.
Wish you a great health!