Uneven pumping question

Kris🐶🐶👶🏼
My right breast is doing great but my left one seems to be slacking. In 7 minutes righty filled a 2.5 oz bottle but lefty has only gotten about 1.5. What can i do to even out production? 
My left boob is starting to hurt sometimes too bc i guess its not getting emptied.
AND when i do breast feed the left is my babies preferred side. 

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