Just eat healthy and as long as your baby is growing youll eventualy put on weight not everyone gains accordingly weare all built differently. I am almost20 weeks pregnant and have only recently gained a lil bit of weight.
If you don't have an appetite, try some grapefruit juice. It always helped me with the nausea and made me hungry during my pregnancies.
do you eat a lot during the day? did you ask your doctor why you're still losing weight? are you constantly exercising?
i didn't start gaining weight until i was about 18-19 weeks along. as long as the baby is healthy and gaining weight, i wouldn't worry too much.
And just keep eating a lot during the day. sneak a few snacks in the middle of the night if you wish.