Hello Doctor , I Am 27 Year Old I Am

Hello Doctor ,

I am 27 year old I am pregnant continuing my 18th week pregnant , Every thing was normal till now but just before two days I went for checkup and my doctor done the ultrasound and told me my water level is very low and she told me to Take glucose and Enoxaparin Injection ( Lonopin) for fifteen days , so please suggest me what to do and why this problem occurred how can I increase my water level .
Please Suggest me

Thank You