I did mine on my own. You do need your Dr on your side!
Here is a write-up from our member Butterflake that is quite helpful.www.healingwell.com/community/default.aspx?f=29&m=2485076
Not everyone gets it on the first try, it is not unusual to be denied twice and the third time you have to go before a judge - I did get an SSD attorney for the hearing. There are laws limiting how much they can charge you.
In some areas the backup at SS can be quite long. If I remember correctly, it was something like 26 months here in Atlanta, Ga - one of the longest in the US.