Terrible Employable History (undiagnosed ADHD)

I have not been formerly diagnosed with ADHD -- currently taking Prozac & Risperidal for Depression however but my employment history is terrible. I am 36 years old, possess a BA & MS degrees in fields that are in demand but haven't held a single job longer than a few months since around 2007.. Since then I have been on many interviews and temporary jobs (that just end abruptly after a few days or weeks). The last full time perm job I had was back in 2009 which I got fired from that November due to performance issues.
At one temp position which I held for a total of 3 days at the end of last year (before getting a voicemail at 6:30pm at night telling me that my assignment was over & not to return) I thought I was doing well but after connecting with another temp from the same agency (who also got let go after 3 months) he told me that one of the co workers said that they determined after 2 days that I wasn't 'interested in learning the systems', & 'I wasn't grasping the work'. I was shocked and couldn't understand how they would reach such a conclusion since they told me that I was picking up the stuff well. During that week I didn't have a chance to see the psyc doc so I didn't take the Prozac for 3 days - maybe withdrawal symptoms?
I will write more later but as crazy as it seems I am looking at either self employment or purchasing an existing business. I am on a temp job now supposed to last for 3-6 months and I actually made it through 2.5 consecutive work weeks!