Weight loss during pregnancy

Nancy
Hello! I am 17w5d and had my monthly check up with my doctor yesterday and as usual, I was weighed in. I had lost 4 pounds since the last time I was there last month instead of gaining and the doctor seemed to be a little concerned but not too much! What can be causing my weight loss if I'm eating regularly and constantly keeping track of my food intake? I don't want to worry myself, hurt my baby, or worry my family! Doctor said it's okay, but if I keep losing weight it's not good 😔