I'm 30 weeks pregnant with twins and I've only gained about 20 lbs. I gained about 80 with my first 2 single pregnancies. My Dr told me I need to put on an extra 15 lbs to catch up to where I should be with twins. Ive been trying but to no avail. Then I just had my growth ultrasound and they said the babies are growing fine. They're actually measuring about a pound more than average. So why do I have to keep trying to eat so much it makes me sick?