I'm afraid I have no advice other than - from what I've heard most women experience better supply from one booby than the other. For me righty was always the best, and even now I've stopped feeding/pumping my right boob is larger.
You could possibly try extra pumping from the with the smaller supply, ie.. pump til the right one is empty, pump til the left one is empty, then pump from the right one again for 5 or 10 minutes, this might give that one the signal that it needs to up its supply.
But to be honest hun, it was just something I got used to x