Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. what I would have been worried about possibility of infection. A well working suddenly becoming painful in my experience usually due to infection. it could be subtle infection not leading all florid symptoms.Other diagnosis I would think of aspetic loosening of implants. Dvt could be there but such a long history usually rare. Sir do consult your operating surgeon or nearby orthopedics surgeon so that he can address your problem early without further damage. Hope I have answered your query. Let me know if I can assist you further.