I've had tailbone pain just about my whole pregnancy. It was only when I was sitting on it though so I never thought much of it. My hips just recently starting aching like in the last week. I'm 40w1d. I think if you're already having these problems then you should take having twins advice.
You should go see a physical therapist. When your pregnant everything loosens up. This can cause your hips and pelvic bone to become uneven making it painful to walk. Some women get it worse then others. I had it kind of bad. Make sure you see someone who works with pregnant women. Good luck to you.