I think the waddling can also be a sign that you may have some pelvic instability. I was told by a friend that I already had the waddle when I was about 16 weeks, and now (24w) I have a lot of pelvic pain and some lower back pain too - which I fear may be SPD...

Id just mention it to your doc/midwife and see if they think it's just a gravity thing or if you might need some advice/support from a physio to stabilise the pelvis to cope with bub's growth.