17+1 feel like I'm tiny

16week

I feel like I am to small for second baby my belly I feel is just not growing. I'm not sure if I feel baby or if it's just gas which has me concerned. I have an appointment tomorrow but I can't help but feel like I'm going to go in and they are going to say baby is gone. Last appointment was little over a week ago and babies hb was in 150s I'm just a nervous momma over here as this is my rainbow and have had some problems with the pregnancy already and scared

17+1