Pumping is taking forever!

My son is almost 6 months old and is still exclusively on breast milk. When I'm at home I breastfeed him 99% of the time on the demand. Of course when I am going to work he takes a bottle which is breast milk. The issue I am having is that it seems to take extremely long pumping sessions to get enough milk. I have a wearable pump that I use at work and it seems to work just fine. My only issue is how long it takes the milk to come out. Sometimes if I pump for 30 minutes I'm lucky if I get 1 oz from each side. Usually what I end up doing is pumping for an hour and a half in the morning with small breaks every 30 minutes from like 10:00 a.m. to 12:00 p.m. This yields 5½-7 oz on average.  My son's last nursing was between 7:30-8:15.  Then I generally pump again from 3:00-5:00 the same way which yields 4½-6 oz.  So all total I've actively pumped 3 hours to get 11-14 oz of milk.  Is it normal for it to take this long? I know it can vary a lot person to person but is there anyway I can do this more efficiently because the long pumping periods make it more difficult to get my work done. I am a dog groomer and there are certain tasks that I cannot do while wearing the pumps for fear of spilling the milk.