How to tell if baby bump is "all baby" or if it is more water and placenta?

Mine is like a rock all the time and has been since about 30 weeks...Im 34 weeks now and the only time it feels different is whn a foot or an elbow suddenly sticks out....I wondered if everyones bump goes rock hard towards the end? Or are some more squashy? Weird Q I know but I have nothjing to compare to...they dont do scans and things at this stage in the UK unless you pay for it....