sudden dip in supply? exclusive pumping

I've been ep'ing for 8 months with no problem but now in the last week my right boob which used to be my major producer is making almost nothing. I'm getting half what I used to get. The left one is still making the same amount as before. Any advice? Why would I have a dip on just one side?! Desperate to get it back up as I'm barely making enough to keep up with baby and want to last another 4 months!