Cramping at almost 35 weeks ... advice please x

Lois

So over the last couple of days I've been having period pain type cramps on and off. Today noticed them the most, they can last anything from 2 minutes-20 minutes but theres no pattern. I get them the most when I stand up from sitting. It's painful but not agony and I don't seem to tighten at the same time.

What could this be??? Any ideas? Thanks xx