Exclusively pump and milk comes out so slowly?

My baby is nearly 6 months and I have been pumping with some formula supplementing for this whole time. For a while I got really lazy and only pumped 3 times a day but still made about 30oz and now I'm trying to increase my supply by pumping much more frequently. But since nearly the start of pumping my milk has always taken a LONG time. I'm talking maybe 45 mins to 1hr to empty. It didn't matter so much when I was only pumping 3 times a day and making 10oz per session, but now as I pump maybe 2oz per session it still takes about 35mins and I still dont get empty. Help? What the heck is wrong? I have Medela pump freestyle and according to the flange pictures those are the correct size + the membranes are brand new.