I applied for SSDI and was approved the first time--within 3 months. I had been dx for over 12 years, worked for 36 years. I applied online --had every health record--and it took about 12 hous of time, because I did have all the information. For a few years I kept a diary of symptoms on a calendar--just jotted how I was feeling, my shots, was I fatigued etc.
I copied all of the records, my diary, and took my birth certificate and ID to the SS off office and dropped off the papers.
The following week I recieved record releases to sign, a phone interview, and completed the forms about daily living. The next time I heard from anyone--I got my approval.
SS only asks for your records for the last three-six months, so you have to be seeing your doc during this time, or at least it is helpful to have his/her support to file. Having worked in HC for years--I wanted to be sure the info got there. I sent everything, organized according to years and exam types. The doctors are busy and disability claims are often last on the list of what to get done.
Hope this helps, and good luck.