I've had this on and off. Advice I've seen that works a bit for me is kind of rock backwards and forwards while you're sitting on the loo. That way, if the baby/your uterus is pressing awkwardly on your bladder and causing the problem it kind of moves the pressure a bit to let you wee. HTH.
I actually sort of stand/ squat and lean forwards. This takes the pressure of uterus off bladder/ urethra and seems to allow a 'free flow'. I'm 34 weeks and have weed like this for weeks! I'm hoping it is toning my thighs a little at least..