You should find out exactly what the number was. The range that is considered normal is pretty vast. In the third trimester it's between 5 and 25.
I was just told it was low. I have been drinking loads of water
Take it easy and drink lots and lots of water. I had low fluid with my first and she was monitored throughout my pregnancy. At 40wks3 days I had an ultrasound that revealed no fluid. I had an emergency c-section and she was born 4 lbs 15 oz 18 1/4" inches. They opted for c-section becuase she was breech.
It's possible that your fluid level can go back up, just make sure to stay plenty hydrated. Did they tell you what your amniotic fluid index was? A smaller baby doesn't necessarily mean an unhealthy baby. My daughter was small and had to be in NICU til she reached 5 lbs. She had some trouble coordinating her sucking/swalling so she was tube fed the first day or so-after that she was fine. She is now 14 and healthy as can be!