Hard to judge by pics, but the domes look a little small for you. Are your breasts completely filling the domes when pumping? If so you should go to a larger size. You can use a belt or some other method to wrap around both domes and pull them closer together. You say you are pumping 5 hours, is this continuously? I agree many hours a day helps, but max 1/2 hour before you take them off and do a quick massage before continuing, especially around the edges and even 15 minutes is better. Also if you can break up the 5 hours or so as being some in morning and the rest in afternoon and evening. Now I know you can't do this while sleeping, but usually any overnight noogling is done a lower pressure. Since you say overnight noogling is done one breast at a time it should be easier to pull it away from your armpit area.
I repeat, quit pumping until the nerve problems completely go away. But continue to massage with Almond oil or whatever is your favorite.