Weird feelings down there (31w)

Mvs01 • #1 is due 31 July 👶🍼☺️
I was sitting on the tube/train into work this morning and felt like someone was knocking on what I imagine was my cervix (very strange feeling) then it felt like something was coming out - like liquid or something. I had a mini panick that maybe it was my waters breaking/leaking but when I got to work and checked there was nothing. 
I seem to have been getting it intermittently over the last week or so but not as strong as it was this morning. Anyone else experiencing something similar? Thank you!