Feeling invalid

My sweet daughter was born a week ago, and I was super eager to be breastfeeding, taking care, and loving her. But, then I found out she was dehydrated and dropped more weight than she should’ve, she wasn’t getting enough from my breast. She usually wants four ounces but I’m only able to make 1.5 ounces. My mother and relatives all think I’m just lazy since I started pumping. They all say to just keep trying, even though I keep telling them that my body won’t make the amount she needs. I feel like a failure and no ones listening to me. It’s not my fault, but it sure feels like it is :(