I have SPD, too, and I'm seeing an osteo now, after being dissatisfied with the prognosis from physios.
Firstly they said it would go away after the birth, but it came back! Second, and much later in the treatment, I get told that for as long as I am BFing I will have relaxin released in my system, so basically 'live with it' but manage my movements.
Not happy.
So, finally went to the osteo who said that you can actually start managing it during pg (physio's tell you to keep your legs together and wait till after the birth) with exercises. I have been given exercises to do and had my hips but back into alignment.
Mind you, my SPD started before 30 weeks, so your sensations may be due to how close you are to birth. SPD is EARLY loosening of that pelvic joint.
You can also get a brace to keep your hips stabilised.