I am on SSD, and my lawyer got 25% of my children's and my back pay. A piece of advice I'd like to give if you don't mind - make sure that your lawyer does only SSD cases, it makes a huge difference. I was one of the lucky ones that got approved on the first try, and I give a great deal of credit to my lawyer for that.
I wish you well and hope that you get an answer quickly and that it is a postive one!
P.S. Straydog is definitely the one to answer any questions related to SSD as she used to work for an attorney that did this type of law.