Congratulations on the birth of your twins and Happy Mother's Day VroomieMama!
I exclusively pump and have been for over a year. I struggled with supply a bit at the beginning and occasionally over the last year and below are a few things that I noticed. Every mama is different, so these may or may not be true for you, but in case they help, here they are:
--For me, stress was the number one thing that seems to reduce my supply. When I pump and am thinking/worrying about how much milk I'm going to get *while* pumping, I tend to get less milk. I've found that when I'm focusing on something else while pumping, I get a lot more milk. I have a hands-free band, so I can do a lot of other things while I pump. Some of the things I like to do while I'm pumping are: watch/talk with my partner and daughter if they are awake (I do pump at least once while they are sleeping); catch up on emails or other online stuff; read or watch TV; make phone calls; play a game; write thank you notes or other correspondence; during the holidays, wrap presents.
--In the beginning, I did jot down how much I pumped each time I pumped and what time it was. it provided an objective measure of whether or not my supply was increasing, but I was careful to look at it in a big picture...seeing the trend over a few days rather than a just pump-to-pump
--Reduced fluids seemed to really reduce my supply. Every time my supply has declined a bit, I've increased how much water and other fluids I'm drinking (even if I'm not thirsty) and that really seems to help.
--Increased protein seems to help. When my supply declines a bit, I try to increase my intake of protein and that usually helps.
--Rest. When I'm tired, my supply always declines a bit. This was especially hard during the newborn time, but as my daughter slept more at a time, I slept more at a time which in turn seemed to increase my supply.
--Being sick. Everytime I've had a cold or something, my supply has decreased a bit, but increases when I get over the cold or whatnot.
--Switching pumps and settings on the pump. I have 2 pumps at home, but I primarily use the hospital-grade Medela Lactina. I used a different hospital-grade one when I was in the hospital; I think it was the Medela Classic. (I know you mentioned that you were using a hospital-grade one, so I hope that helps!) I definitely found the hospital-grade pump much better than the personal pump, but what I really found made the different was experimenting and varying the level of speed and strength of suction. On the hospital-grade pumps these are separate dials and adjusting these independently really helped me. The personal pump I have (the Medela Pump in Style Advanced) has one control that adjusts both the level of speed and strength of suction and isn't nearly as good for me.
--Pumping more often and pumping for a few minutes past when I'm not getting anything (but not so long that I get sore).
I'll thinking of you and hoping for the best for you!
PS Yes, I'm pumping while I posted this!