Hi Lynne,
I've have this problem also. I have Carpal tunnel syndrome so any pressure on my hands and they go numb. What helped me was putting an extra set of brake levers on the tops. I tend to ride there the most and constantly switch between those and the hoods. Changing hand positions helps a lot. I also wear gloves with gel padding in them and I use Phat bar gel and tape from specialized on the bars. At night I wear a hand brace that keeps my wrist from bending. You can find them at most drug stores. I had a few weeks where I couldn't shift either. It is really frustrating. Some tweaking of the derailer helped and maybe playing with the position of your handlebars and hoods may also help.