Does lower pelvic pain at 28 weeks pregnant mean that the baby is turning or changing positions?

It could mean that the baby is dropping or changing positions, yes. It could also mean a number of other things! But if the pelvic pain lasts for a few hours, if it's painful enough that you have to change your breathing pattern or feel you need to sit down, if you're having a strange coloured or smelly discharge or spotting then see a doctor. You may have a urine infection, get that checked, or it may be your ligaments relaxing from the pregnancy hormones, this happened to me in my second pregnancy at 28 weeks and after that I couldn't walk more than a couple of hundred yards because of the pain. A physical therapist can prescribe a belt to support your pelvis if this is the case.