Low amniotic fluid

Hi all! I'm new to this app, but my friend told me how great it was and I should post on here about my pregnancy. I'm 19years old and currently 32 weeks and 4 days pregnant with my little girl(my first pregnancy). At 19 weeks they noticed I had a lower AFI(amniotic fluid) and started to monitor it every week. Since then it has stayed between 7.7 and 8.8. Which is amazing! 8 was just below "normal" the past couple weeks. Well last week at my ultrasound they informed me that it had dropped from 8.8 to 6.3 in one week. I have been drinking 4 liters of water every day and watching my diet. I just want to hear from moms who went through the same situation as me and what happened. They also said she is measuring on the petite side which leads them to believe it's my placenta not working 100% but the blood flow in the cord is perfect. 
Thanks (: