Is there any changes in your life now that brought about this change? Period or stress may cause changes in supply.
Perhaps you can try power pumping or increasing the pump frequency to help bring the supply back up? Also, can also consider milk boosters such as oats/oatmeal, milo, salmon, fenugreek etc to see if any work for you.
Get plenty of rest, eat well, and stay hydrated. Hopefully, the change is just temporary. Take care mummy!