This is an extremely complex issue. Feather picking could be caused by parasites, mites, other skin infections, gastrointestinal issues and many other physical causes. It can also be caused by many behavioral problems, such as boredom, separation anxiety, stress and more.
This must be addressed by a veterinarian that is board certified in exotics. Please refer to the following web site for an Avian Vet near you: http://www.aav.org/index.php
I spoke with a friend of mine who does parrot rescue and also has 9 parrots of his own. Of course the first thing to check for is parasites. But when you mentioned that you've been working a lot, it may be loneliness and boredom. He's had your attention and is now left with too much free time, not sure what to do. A couple things that were suggested are more toys to play with, taking strips of lettuce or some kind of food that you can hide around areas in his cage or weave through the bars so he has to work at getting them out. He needs challenges and enrichment. African Grays are one of the smartest parrots around and he needs to interact with someone or something.