It could be the baby being head down.
I'm 37 weeks 3 days and lately I've been having sharp pains in my pelvic area so I asked my ob about it and she says it's due to cervical thinning and also because the baby's head is positioning in the birth canal .
It's normal I'm 31 weeka also and I've been feeling tje Same thing I had my 32 weeks appointment today and my doctor told me baby was head down that's why I have pressure