I am on SSDI (have been for awhile), went through Vocational Rehab over the last several years to get retraining by going back to school for a different degree, just graduated in May, passed my boards, and finally got the courage to find a job in July (after not working for 14 years), which I started at the end of July.
The gap in my work history could be explained to potential employers because, I did not tell them about the MH illness but, I took the time to care for my ailing grandparents and to go back to school. In your case, you took time to care for your family to explain the gap.
I was motivated by three things: 1. to be self-supporting and independent, 2. the need for more money, and 3. to prove to myself for my self esteem that I could do it again; I too was feeling worthless without a job. It has been with quite a few struggles but I am getting through the days so far.
I would recommend you talk with your local social security office or go online to get the information about returning to work as there are guidelines and policies as to how income can affect your social security, the trial work period months, reporting income, loss of benefits after this trial work period, and the reinstatement period after the trial work period should something happen to aggrevate your disability that you cannot work (which is 36 months after the trial work period ends). After that is when you have to start from scratch to refile as the above poster mentions. It is important to know all this information so you don't loose your benefits prematurely. This is the brochure that talks about it directly from Social Security.:
http://www.ssa.gov/pubs/EN-05-10095.pdf
If you have any questions after reading this, contact them.
I wish you well as you move forward. Hang in there meanwhile.