Kneecap replacement surgery

Hi I’m 51 I had arthroscopy two and a half years ago and a partial knee replacement 18 months ago all was great I have full bend in my knee can walk for miles walk upstairs without pain and have been Zumba and kettle size classes since January up until now my knee is painful fairly tender it feels tight hurts to walk and painfully going up stairs has anyone else suddenly had problems this far down the line when things seemed to going do well xx thank you in advance for any replies