Worth bringing up with your midwife as you may be able to get a referral to a physio who could give you some tips to avoid inflaming it. Chances are, it's, unfortunately, normal. Increase in the hormone relaxin makes your joints more flexible (for the purposes of birthing and accommodating a growing bub) but also comes with aches and pains, commonly in the pelvis. I had it mildly with my first, and quite badly with my second. Nothing 'helped' as such, but avoiding certain types of movement stopped it flaring up, and wearing a broad brace (just made out of wet-suit material) around my hips stopped the joints from separating as much, and was a great reminder to not do the movements that made it worse.

Best of luck!