Melek, I beleive in part it depends on how long you have worked. I think the SS Admin looks at "credits" for time worked, but I am not sure how that works. You might be able to find that out just by calling the Social Security Administration. And remember, there is a difference between Social Security Disability and Supplemental Security Income (which you can get when you income falls below a certain level, even if you don't get SSD).
One of the first criteria is that you are not working. Unfortunately, you said that, in spite of your under-performance and your employer's dissatisfaction, you are still working. According to everything I have learned, this will be a major issue, because SS considers you disabled if there is no work you can perform anywhere in the US labor market with your medical condition. I think you may benefit from a meeting with an attorney to see where you stand right now. . . .
A couple articles that might help you in your investigation:
http://arthritis.about.com/cs/disability/a/ssdi.htm
http://www.socialsecurityhome.com/re...%20A%20Credit?
This article claims to contain a FREE disability evaluation (questions) to help you assess your chances:
http://disabilityblogger.blogspot.co...isability.html
Good luck. I was somewhat in your position in that my employer
said that they would accommodate my reduced capacity, but when push came to shove, I probably would have been fired had they not put me on LTD based on the combination of all the effects of my condition, including lack of sleep, unusually excessive need for breaks, and disruptions to my work flow when I was in flare-up. Perhaps you could benefit from talking to your HR person as well, just to see if they could offer any help.