my doctor won't tell me what I am having til I'm at least 18 to 20 weeks. the anticipation is…

my doctor won't tell me what I am having til I'm at least 18 to 20 weeks. the anticipation is killing me I'm 16 weeks and 3 days today. this is my first child and I haven't gained any weight I've lost over 20. anybody know what I can do i feel like the baby isn't getting enough nutrients since I am losing weight.