2 more c from an old mom: Yes, your joints, especially pelvic joints, do loosen up more and more through pregnancy. Also yes, you can wind up with chronic hip and/or back pain. I've never heard of biking being an issue, though I don't have the knowledge to say it isn't for sure. Most of those I've heard of or known to have chronic pain post-partum have had some serious hip and back pain issues during late pregnancy as well. Some have been pretty much unable to walk, so they for sure weren't biking either. I would definitely advise leaving off biking if you notice it's hurting. But I also have some positive advice to give:

In my second pregnancy I was experiencing some of this hip pain. This was already at 4 months, so I was worried it would get worse and maybe become chronic. My doctor, like most, pooh-poohed it as a normal complication of pregnancy, nothing to do anout it. But as luck would have it, I worked in the same building as the company's health services. Our physical therapist saw me limping one day and called me in to show me some exercizes that could help. They did. These are exercizes that strengthen the "girdle" of muscles surrounding the pelvis, but without moving the pelvic bones in the process. That way your pelvic muscles take over some of the stabilization that the bones usually provide. It also helps restabilize the bones post-partum. The exercizes are isometric. Sit with your legs outstretched, strap a belt around your ankles and, with one fist between your ankles, tighten the belt to hold that distance. This keeps your hips in a neutral position, perpendicular to the axis of the pelvis when your legs are straight. Now lie back and, with your legs straight, press outward against the belt horizontally (i.e. straight out to the right and left) and vertically (pressing one foot up while holding the other down, then change feet). I don't remember whether she also had me do a diagonal press. I do think she had me roll over and do some of these presses lying on either side and on my tummy. You should probably ask a physical therapist near you whether I'm remembering all this right. My "baby" is 23 already, so this was a long time ago.