Sleeping discomfort

Currently 25 weeks. Have been religiously sleeping on my sides since 15 weeks or so. But these few days I am experiencing discomfort. The side that I am lying on will start aching after a while (especially the side butt cheek area). This has resulted me in flipping numerous times throughout the night and hence not getting a good night's rest. Is there any way to alleviate the discomfort? Or is this just part and parcel of pregnancy? 😢