Pressure that hurts

Jamie • We have a 12 year old boy, 10 year old girl, 11 month old twin boys and 1 month old twin girls.
I'm 31 weeks pregnant with twins and I've used the bathroom twice today and since then I've been having pain in my rectum area. It hurts no matter what position im in and it feels like there's pressure. Has anyone experienced this or know what it could be?