Weight gain

As anyone had this problem I'm  30 weeks and 4days I haven't gain any weight I thought I gain 7lb but my doctor told me I haven't gain anything and she's sending me for a ultrasound to see how much the baby weigh is I was trying to tell her that's how it's is with my pregnancy I lose weight before I gain anything this my 5th pregnancy but she's not listen to me and it has me scared on what's going to happend