question for plus size moms and moms to be..

I'm a size 20 (I know I plan on going on a weight loss journey once baby is here.) and my grandmother told me I didn't need maternity clothes. She says because I'm already fat I won't show so all my clothes will fit fine. Well I'm 16 weeks now, and I know to everyone else i just look like I've gained even more weight but I've actually lost weight with this pregnancy and my pants barley button. Did any other plus size women have this issue? My grandmother says it's all in my head. So know I just feel fat and uncomfortable with myself.