Bump not growing :(

So my bump is the same as it was 4 weeks ago :( at my last doctors check up, I measured 3 1/2 week small (fundal height was 27cm and I was at 31 weeks 1/2), and also had decreased HcG in the first trimester, which could be an indication that baby will be small (surprising, considering I'm 5'10" and the father is 6'2"). I have an ultrasound planned on Thursday to see how big (or small) baby is... but I'm really worried in the meantime.

Anybody else had something similar? If so, what happened in the end??