Any Postal workers ever gone through disability retirement?

I've been a letter carrier for 18 yrs. and walked 15 miles a day for the past 15 yrs. while carrying a 35 lb. bag on my shoulder through rain sleet snow and heat. up a mntn. of steps everyday. well- my knees, ankles and feet finally gave into major arthritis complications. Now, after 18 yrs. of loyal service, they are puttiing me through the ';ringer';. I've submitted major medical documentation of my condiition and they tell me it could take up to 6 months before I MAY recieve a check! Has anyone been through this, or do you know of anyone that has?