supply suddenly uneven - what gives?

kmm2150

Usually when I pump I get about the same from each side, sometimes a little more from one that the other but nothing too noticeable and not always from the same side.  Yesterday, I had to just use my little hand pump and noticed that, in the 3 times I pumped, I was getting less than half on my left than what I was getting on my right, but kind of thought, well maybe it's the hand pump, something about the way I'm using it.  Just pumped this morning with medela pisa and it was the same thing - less than half on my left than what I got on my right - why could this be happening? 

If dd only takes one side, it usually is the left side (the one with less), because the right has a more forceful letdown and she fusses and pops off a lot, so she seems to find the left more soothing.  Because of this, I sometimes end up pumping on the right 1-2 times in the evening and once over night for my own comfort.  I could see the pumping making my supply go up, but it seems like supply on the other side has actually gone down!  Help!