Or, it could be a physical issue like constipation, which puts pressure on the bladder. (happywithbaby.com)
As your pregnancy progresses, baby will get bigger and put more pressure on your bladder, so you might as well get used to making multiple trips to the bathroom. (thebump.com)
At this stage of pregnancy you may be experiencing it more as your baby is putting a lot of pressure on your bladder. (bounty.com)