17+weeks pregnant pressure low down

hi ladies, 

im 17+6 weeks and I'm feeling pressure in my bottom (sorry tmi) and low down in my vagina. I know that baby is really low down because I can feel him/her and midwife found heartbeat yesterday just above my pubic bone. Just wondered if anyone else experiened this? this is my second baby and my first baby was 8lb15 very big as I'm only slim and 5ft1. I'm going to call midwife tomorrow if nothing has changed. Just wondered if any other mums had had the same feeling. thanks in advance