I went to a physio when I was pg with DD1, and they gave me some excellent stretches to ease the tension in the glutes and having the muscles more stretched and supple really helped. Sit with your knees at right angles and your back straight. Put the ankle of the most sore hip on the opposite knee, and then using your hands press the knee of the sore hip towards your chair. This will stretch the muscles from your lower back to your knee, and you will feel that the sciatic area is one of the areas that is stretched. It may also be worth getting some tubi-grip or a support belt for the times it is at it's worst, just to hold the hip socket in the best position and reduce the pain.