need some advice please

I had arthroscopic opp 12 weeks ago to find out why knee hurt so much after opp was told had grade 4 ostioarthritis would need more surgery in time does any one now why. also i have less movment to my knee now than before the opp and more pain still cannot go up and down the stairs if anything it is worse. my doctor tells me i should be patient. My sick note runs out in a week dont now if i should go back to work I am a cook i am really worried as my knee also gives way tat is getting worse i really dont now whot to do would be gratful to any help.