For no known reason, in my last pregnancy I had PROM at 15 weeks and lost almost half the fluid. I know it is a different stage of the pregnancy and probably everyone is different but I rested for a week, took the time off work, sent the toddler to the MIL and drank as much fluid as I could and when I went back for a scan the following week the level was an acceptable amount. She was born at 37w 5 days and ok, although almost a kilo smaller than my DS born at 38wks.

Only letting you know what worked for me.
Goodluck I hope everything goes ok.