How Long Should I Rest After Surgery For Rotator Cuff?

I had shoulder surgery for bone spurs and torn rotator cuff in August. I am in more pain now than before the surgery. I am 53, female and otherwise healthy. I am a postal clerk in a very busy office, constant reaching to put up mail, pushing and pulling very heavy mail cages, lifting bags of parcels approx. 100 lbs, etc etc. How likely am I to be able to return to work and how long before doing so? I have severe shoulder pain, no backward range, can t sleep, actually can t do anythng more than about an hour before having to just rest. I only have 2 more years to be eligible for retirement. Would disability be possible?